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FA-58626 / Loan amortization schedules / Open access

Rule of 78s early payoff rebate: acquisition fee exclusion · case 01

The fully earned acquisition fee is partly rebated.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The rebate base includes the acquisition fee.

VERIFIED REPAIR

Exclude the acquisition fee from the rebatable charge.

Unsuccessful approach: Excluding only a prorated share of the fee still rebates part of it.

Case contract

x = {'term' n, 'paid' k, 'finance_charge', 'acq_fee' (fully earned up front), 'payment', 'min_rebate'}. Rebatable charge = finance_charge - acq_fee; remaining r = n - k; rebate = round_half_up(rebatable * r(r+1) / (n(n+1))), set to 0 when below min_rebate. Payoff = payment*r - rebate; earned = finance_charge - rebate. Return {'rebate', 'payoff', 'earned'}.

Why this case matters

Amortization engines drive borrower statements, payoff quotes and investor remittances; a misplaced rounding step, boundary or ordering rule compounds across hundreds of periods.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    n = x['term']
    k = x['paid']
    fc = x['finance_charge']
    rem = n - k
    rebate = rnd(fc * rem * (rem + 1), n * (n + 1))
    if rebate < x['min_rebate']:
        rebate = 0
    remaining = x['payment'] * rem
    return {'rebate': rebate, 'payoff': remaining - rebate, 'earned': x['finance_charge'] - rebate}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: acquisition fee exclusion', {'term': 36, 'paid': 18, 'finance_charge': 50000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 100}, {'rebate': 10912, 'payoff': 439088, 'earned': 39088}], ['control 1', {'term': 36, 'paid': 35, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 180, 'payoff': 9820, 'earned': 119820}], ['control 2', {'term': 36, 'paid': 35, 'finance_charge': 50000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 25000, 'earned': 50000}], ['control 3', {'term': 24, 'paid': 23, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 25000, 'earned': 100}], ['control 4', {'term': 24, 'paid': 12, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 100}, {'rebate': 13000, 'payoff': 287000, 'earned': 37000}], ['control 5', {'term': 12, 'paid': 3, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 100}, {'rebate': 0, 'payoff': 38889, 'earned': 100}], ['control 6', {'term': 6, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 500}, {'rebate': 2222, 'payoff': 27778, 'earned': 5555}]], [['regression: acquisition fee exclusion', {'term': 36, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 500}, {'rebate': 4445, 'payoff': 325555, 'earned': 3332}], ['control 1', {'term': 24, 'paid': 1, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 500}, {'rebate': 110400, 'payoff': 464600, 'earned': 9600}], ['control 2', {'term': 12, 'paid': 1, 'finance_charge': 100, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 110000, 'earned': 100}], ['control 3', {'term': 24, 'paid': 24, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 0, 'earned': 120000}], ['control 4', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 900000, 'earned': 100}], ['control 5', {'term': 24, 'paid': 12, 'finance_charge': 100, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 120000, 'earned': 100}], ['control 6', {'term': 6, 'paid': 0, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 500}, {'rebate': 7777, 'payoff': 52223, 'earned': 0}]], [['regression: acquisition fee exclusion', {'term': 6, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 0}, {'rebate': 79, 'payoff': 12884, 'earned': 7698}], ['control 1', {'term': 6, 'paid': 5, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 25000, 'earned': 100}], ['control 2', {'term': 24, 'paid': 3, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 92400, 'payoff': 117600, 'earned': 27600}], ['control 3', {'term': 12, 'paid': 3, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 2000}, {'rebate': 28846, 'payoff': 10043, 'earned': 21154}], ['control 4', {'term': 6, 'paid': 5, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 0}, {'rebate': 5714, 'payoff': 4286, 'earned': 114286}], ['control 5', {'term': 12, 'paid': 12, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 0, 'earned': 7777}], ['control 6', {'term': 24, 'paid': 24, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 10000, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 7777}]], [['regression: acquisition fee exclusion', {'term': 24, 'paid': 12, 'finance_charge': 120000, 'acq_fee': 2500, 'payment': 4321, 'min_rebate': 100}, {'rebate': 30550, 'payoff': 21302, 'earned': 89450}], ['control 1', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 900000, 'earned': 100}], ['control 2', {'term': 12, 'paid': 12, 'finance_charge': 50000, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 50000}], ['control 3', {'term': 12, 'paid': 0, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 2000}, {'rebate': 7777, 'payoff': 44075, 'earned': 0}], ['control 4', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 0}, {'rebate': 100, 'payoff': 359900, 'earned': 0}], ['control 5', {'term': 6, 'paid': 3, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 75000, 'earned': 100}], ['control 6', {'term': 36, 'paid': 18, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 0}, {'rebate': 12838, 'payoff': 64940, 'earned': 37162}]], [['regression: acquisition fee exclusion', {'term': 24, 'paid': 12, 'finance_charge': 120000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 29250, 'payoff': 270750, 'earned': 90750}], ['control 1', {'term': 24, 'paid': 12, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 500}, {'rebate': 0, 'payoff': 51852, 'earned': 100}], ['control 2', {'term': 36, 'paid': 36, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 100}], ['control 3', {'term': 12, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 300000, 'earned': 100}], ['control 4', {'term': 12, 'paid': 12, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 0, 'earned': 7777}], ['control 5', {'term': 24, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 0}, {'rebate': 100, 'payoff': 103604, 'earned': 0}], ['control 6', {'term': 6, 'paid': 5, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 100}, {'rebate': 0, 'payoff': 4321, 'earned': 100}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: acquisition fee exclusion{'earned': 37162, 'payoff': 437162, 'rebate': 12838}{'earned': 39088, 'payoff': 439088, 'rebate': 10912}Failed
control 1{'earned': 119820, 'payoff': 9820, 'rebate': 180}{'earned': 119820, 'payoff': 9820, 'rebate': 180}Passed
control 2{'earned': 50000, 'payoff': 25000, 'rebate': 0}{'earned': 50000, 'payoff': 25000, 'rebate': 0}Passed
control 3{'earned': 100, 'payoff': 25000, 'rebate': 0}{'earned': 100, 'payoff': 25000, 'rebate': 0}Passed
control 4{'earned': 37000, 'payoff': 287000, 'rebate': 13000}{'earned': 37000, 'payoff': 287000, 'rebate': 13000}Passed
control 5{'earned': 100, 'payoff': 38889, 'rebate': 0}{'earned': 100, 'payoff': 38889, 'rebate': 0}Passed
control 6{'earned': 5555, 'payoff': 27778, 'rebate': 2222}{'earned': 5555, 'payoff': 27778, 'rebate': 2222}Passed

SHA-256 / b3bc6de18c4a5f0e6f24653a7466540197de4f31e9b26feb589dc15b7272dbd2

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    n = x['term']
    k = x['paid']
    fc = x['finance_charge'] - x['acq_fee'] * (n - k) // n
    rem = n - k
    rebate = rnd(fc * rem * (rem + 1), n * (n + 1))
    if rebate < x['min_rebate']:
        rebate = 0
    remaining = x['payment'] * rem
    return {'rebate': rebate, 'payoff': remaining - rebate, 'earned': x['finance_charge'] - rebate}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: acquisition fee exclusion', {'term': 36, 'paid': 18, 'finance_charge': 50000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 100}, {'rebate': 10912, 'payoff': 439088, 'earned': 39088}], ['control 1', {'term': 36, 'paid': 35, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 180, 'payoff': 9820, 'earned': 119820}], ['control 2', {'term': 36, 'paid': 35, 'finance_charge': 50000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 25000, 'earned': 50000}], ['control 3', {'term': 24, 'paid': 23, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 25000, 'earned': 100}], ['control 4', {'term': 24, 'paid': 12, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 100}, {'rebate': 13000, 'payoff': 287000, 'earned': 37000}], ['control 5', {'term': 12, 'paid': 3, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 100}, {'rebate': 0, 'payoff': 38889, 'earned': 100}], ['control 6', {'term': 6, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 500}, {'rebate': 2222, 'payoff': 27778, 'earned': 5555}]], [['regression: acquisition fee exclusion', {'term': 36, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 500}, {'rebate': 4445, 'payoff': 325555, 'earned': 3332}], ['control 1', {'term': 24, 'paid': 1, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 500}, {'rebate': 110400, 'payoff': 464600, 'earned': 9600}], ['control 2', {'term': 12, 'paid': 1, 'finance_charge': 100, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 110000, 'earned': 100}], ['control 3', {'term': 24, 'paid': 24, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 0, 'earned': 120000}], ['control 4', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 900000, 'earned': 100}], ['control 5', {'term': 24, 'paid': 12, 'finance_charge': 100, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 120000, 'earned': 100}], ['control 6', {'term': 6, 'paid': 0, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 500}, {'rebate': 7777, 'payoff': 52223, 'earned': 0}]], [['regression: acquisition fee exclusion', {'term': 6, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 0}, {'rebate': 79, 'payoff': 12884, 'earned': 7698}], ['control 1', {'term': 6, 'paid': 5, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 25000, 'earned': 100}], ['control 2', {'term': 24, 'paid': 3, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 92400, 'payoff': 117600, 'earned': 27600}], ['control 3', {'term': 12, 'paid': 3, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 2000}, {'rebate': 28846, 'payoff': 10043, 'earned': 21154}], ['control 4', {'term': 6, 'paid': 5, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 0}, {'rebate': 5714, 'payoff': 4286, 'earned': 114286}], ['control 5', {'term': 12, 'paid': 12, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 0, 'earned': 7777}], ['control 6', {'term': 24, 'paid': 24, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 10000, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 7777}]], [['regression: acquisition fee exclusion', {'term': 24, 'paid': 12, 'finance_charge': 120000, 'acq_fee': 2500, 'payment': 4321, 'min_rebate': 100}, {'rebate': 30550, 'payoff': 21302, 'earned': 89450}], ['control 1', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 900000, 'earned': 100}], ['control 2', {'term': 12, 'paid': 12, 'finance_charge': 50000, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 50000}], ['control 3', {'term': 12, 'paid': 0, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 2000}, {'rebate': 7777, 'payoff': 44075, 'earned': 0}], ['control 4', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 0}, {'rebate': 100, 'payoff': 359900, 'earned': 0}], ['control 5', {'term': 6, 'paid': 3, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 75000, 'earned': 100}], ['control 6', {'term': 36, 'paid': 18, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 0}, {'rebate': 12838, 'payoff': 64940, 'earned': 37162}]], [['regression: acquisition fee exclusion', {'term': 24, 'paid': 12, 'finance_charge': 120000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 29250, 'payoff': 270750, 'earned': 90750}], ['control 1', {'term': 24, 'paid': 12, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 500}, {'rebate': 0, 'payoff': 51852, 'earned': 100}], ['control 2', {'term': 36, 'paid': 36, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 100}], ['control 3', {'term': 12, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 300000, 'earned': 100}], ['control 4', {'term': 12, 'paid': 12, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 0, 'earned': 7777}], ['control 5', {'term': 24, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 0}, {'rebate': 100, 'payoff': 103604, 'earned': 0}], ['control 6', {'term': 6, 'paid': 5, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 100}, {'rebate': 0, 'payoff': 4321, 'earned': 100}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: acquisition fee exclusion{'earned': 38125, 'payoff': 438125, 'rebate': 11875}{'earned': 39088, 'payoff': 439088, 'rebate': 10912}Failed
control 1{'earned': 119820, 'payoff': 9820, 'rebate': 180}{'earned': 119820, 'payoff': 9820, 'rebate': 180}Passed
control 2{'earned': 50000, 'payoff': 25000, 'rebate': 0}{'earned': 50000, 'payoff': 25000, 'rebate': 0}Passed
control 3{'earned': 100, 'payoff': 25000, 'rebate': 0}{'earned': 100, 'payoff': 25000, 'rebate': 0}Passed
control 4{'earned': 37000, 'payoff': 287000, 'rebate': 13000}{'earned': 37000, 'payoff': 287000, 'rebate': 13000}Passed
control 5{'earned': 100, 'payoff': 38889, 'rebate': 0}{'earned': 100, 'payoff': 38889, 'rebate': 0}Passed
control 6{'earned': 5555, 'payoff': 27778, 'rebate': 2222}{'earned': 5555, 'payoff': 27778, 'rebate': 2222}Passed

SHA-256 / 66a4c442c33500de0c305b4ce1cd6d89c504e537bde5470f64ccde1e9f07c1d3

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    n = x['term']
    k = x['paid']
    fc = x['finance_charge'] - x['acq_fee']
    rem = n - k
    rebate = rnd(fc * rem * (rem + 1), n * (n + 1))
    if rebate < x['min_rebate']:
        rebate = 0
    remaining = x['payment'] * rem
    return {'rebate': rebate, 'payoff': remaining - rebate, 'earned': x['finance_charge'] - rebate}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: acquisition fee exclusion', {'term': 36, 'paid': 18, 'finance_charge': 50000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 100}, {'rebate': 10912, 'payoff': 439088, 'earned': 39088}], ['control 1', {'term': 36, 'paid': 35, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 180, 'payoff': 9820, 'earned': 119820}], ['control 2', {'term': 36, 'paid': 35, 'finance_charge': 50000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 25000, 'earned': 50000}], ['control 3', {'term': 24, 'paid': 23, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 25000, 'earned': 100}], ['control 4', {'term': 24, 'paid': 12, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 100}, {'rebate': 13000, 'payoff': 287000, 'earned': 37000}], ['control 5', {'term': 12, 'paid': 3, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 100}, {'rebate': 0, 'payoff': 38889, 'earned': 100}], ['control 6', {'term': 6, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 500}, {'rebate': 2222, 'payoff': 27778, 'earned': 5555}]], [['regression: acquisition fee exclusion', {'term': 36, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 500}, {'rebate': 4445, 'payoff': 325555, 'earned': 3332}], ['control 1', {'term': 24, 'paid': 1, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 500}, {'rebate': 110400, 'payoff': 464600, 'earned': 9600}], ['control 2', {'term': 12, 'paid': 1, 'finance_charge': 100, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 110000, 'earned': 100}], ['control 3', {'term': 24, 'paid': 24, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 100}, {'rebate': 0, 'payoff': 0, 'earned': 120000}], ['control 4', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 900000, 'earned': 100}], ['control 5', {'term': 24, 'paid': 12, 'finance_charge': 100, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 120000, 'earned': 100}], ['control 6', {'term': 6, 'paid': 0, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 500}, {'rebate': 7777, 'payoff': 52223, 'earned': 0}]], [['regression: acquisition fee exclusion', {'term': 6, 'paid': 3, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 0}, {'rebate': 79, 'payoff': 12884, 'earned': 7698}], ['control 1', {'term': 6, 'paid': 5, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 25000, 'earned': 100}], ['control 2', {'term': 24, 'paid': 3, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 92400, 'payoff': 117600, 'earned': 27600}], ['control 3', {'term': 12, 'paid': 3, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 2000}, {'rebate': 28846, 'payoff': 10043, 'earned': 21154}], ['control 4', {'term': 6, 'paid': 5, 'finance_charge': 120000, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 0}, {'rebate': 5714, 'payoff': 4286, 'earned': 114286}], ['control 5', {'term': 12, 'paid': 12, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 0, 'earned': 7777}], ['control 6', {'term': 24, 'paid': 24, 'finance_charge': 7777, 'acq_fee': 7500, 'payment': 10000, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 7777}]], [['regression: acquisition fee exclusion', {'term': 24, 'paid': 12, 'finance_charge': 120000, 'acq_fee': 2500, 'payment': 4321, 'min_rebate': 100}, {'rebate': 30550, 'payoff': 21302, 'earned': 89450}], ['control 1', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 900000, 'earned': 100}], ['control 2', {'term': 12, 'paid': 12, 'finance_charge': 50000, 'acq_fee': 2500, 'payment': 10000, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 50000}], ['control 3', {'term': 12, 'paid': 0, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 2000}, {'rebate': 7777, 'payoff': 44075, 'earned': 0}], ['control 4', {'term': 36, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 0}, {'rebate': 100, 'payoff': 359900, 'earned': 0}], ['control 5', {'term': 6, 'paid': 3, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 75000, 'earned': 100}], ['control 6', {'term': 36, 'paid': 18, 'finance_charge': 50000, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 0}, {'rebate': 12838, 'payoff': 64940, 'earned': 37162}]], [['regression: acquisition fee exclusion', {'term': 24, 'paid': 12, 'finance_charge': 120000, 'acq_fee': 7500, 'payment': 25000, 'min_rebate': 500}, {'rebate': 29250, 'payoff': 270750, 'earned': 90750}], ['control 1', {'term': 24, 'paid': 12, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 500}, {'rebate': 0, 'payoff': 51852, 'earned': 100}], ['control 2', {'term': 36, 'paid': 36, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 0}, {'rebate': 0, 'payoff': 0, 'earned': 100}], ['control 3', {'term': 12, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 25000, 'min_rebate': 500}, {'rebate': 0, 'payoff': 300000, 'earned': 100}], ['control 4', {'term': 12, 'paid': 12, 'finance_charge': 7777, 'acq_fee': 0, 'payment': 10000, 'min_rebate': 2000}, {'rebate': 0, 'payoff': 0, 'earned': 7777}], ['control 5', {'term': 24, 'paid': 0, 'finance_charge': 100, 'acq_fee': 0, 'payment': 4321, 'min_rebate': 0}, {'rebate': 100, 'payoff': 103604, 'earned': 0}], ['control 6', {'term': 6, 'paid': 5, 'finance_charge': 100, 'acq_fee': 7500, 'payment': 4321, 'min_rebate': 100}, {'rebate': 0, 'payoff': 4321, 'earned': 100}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: acquisition fee exclusion{'earned': 39088, 'payoff': 439088, 'rebate': 10912}{'earned': 39088, 'payoff': 439088, 'rebate': 10912}Passed
control 1{'earned': 119820, 'payoff': 9820, 'rebate': 180}{'earned': 119820, 'payoff': 9820, 'rebate': 180}Passed
control 2{'earned': 50000, 'payoff': 25000, 'rebate': 0}{'earned': 50000, 'payoff': 25000, 'rebate': 0}Passed
control 3{'earned': 100, 'payoff': 25000, 'rebate': 0}{'earned': 100, 'payoff': 25000, 'rebate': 0}Passed
control 4{'earned': 37000, 'payoff': 287000, 'rebate': 13000}{'earned': 37000, 'payoff': 287000, 'rebate': 13000}Passed
control 5{'earned': 100, 'payoff': 38889, 'rebate': 0}{'earned': 100, 'payoff': 38889, 'rebate': 0}Passed
control 6{'earned': 5555, 'payoff': 27778, 'rebate': 2222}{'earned': 5555, 'payoff': 27778, 'rebate': 2222}Passed

SHA-256 / 2151e4b33294bcdf616d039c74cae2c9136e6a13427110c4e9d25fdcbf538949

Verification & scope

A deterministic bounded teaching model with stipulated toy lending rules stated in the contract; money is integer cents and rates are basis points; it makes no claim of conformance to any regulation, servicing standard or product. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:46:28.510550+00:00.

Case digest / 1ace4b036469e510950c17a8a2fa45b3594e362baf8eb93a1ce95e8349f2db62