FA-63306 / Insurance premium rating / Open access

Renewal rate capping transition: Upper cap is measured from the indicated premium · case 01

Increases are never capped.

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

ROOT CAUSE

The upper bound is based on the new indicated premium.

VERIFIED REPAIR

Base the upper bound on last year's charged premium.

Unsuccessful approach: Averaging the two premiums still lets increases exceed the cap.

Case contract

Input prior premium (0 = new business), up/down caps per mille, years [[indicated or None for a lapse, coverage_changed]]. A lapse outputs None and the next year is new business. New business or coverage changes charge the indicated premium; otherwise charge the indicated premium clamped to [prev*(1-down), prev*(1+up)] with bounds rounded half-up, where prev is last year's charged premium.

Why this case matters

Transition caps limit renewal disruption and must chain from what was actually charged.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(x):
    prev=x['prior']; out=[]
    for ind,changed in x['years']:
        if ind is None:
            out.append(None); prev=0; continue
        if changed or prev==0:
            cur=ind
        else:
            hi=math.floor(Fraction(ind*(1000+x['up']),1000)+Fraction(1,2))
            lo=math.floor(Fraction(prev*(1000-x['down']),1000)+Fraction(1,2))
            cur=max(lo,min(hi,ind))
        out.append(cur); prev=cur
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['large increase phased in', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[282332, False], [282332, False], [282332, False]]}, [156694, 173930, 193062]], ['large decrease capped', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[70583, False], [70583, False]]}, [134108, 127403]], ['coverage change exempt then capped', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[282332, True], [423498, False]]}, [282332, 313389]], ['new business exempt', {'prior': 0, 'up': 110, 'down': 50, 'years': [[141166, False], [282332, False]]}, [141166, 156694]], ['lapse restarts as new business', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[141166, False], [None, False], [423498, False]]}, [141166, None, 423498]], ['within caps', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[142166, False], [140166, False]]}, [142166, 140166]], ['mixed history', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[172018, False], [166564, False], [197332, False], [213340, False]]}, [156694, 166564, 184886, 205223]]], [['large increase phased in', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[163834, False], [163834, False], [163834, False]]}, [91747, 102757, 115088]], ['large decrease capped', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[40958, False], [40958, False]]}, [77821, 73930]], ['coverage change exempt then capped', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[163834, True], [245751, False]]}, [163834, 183494]], ['new business exempt', {'prior': 0, 'up': 120, 'down': 50, 'years': [[81917, False], [163834, False]]}, [81917, 91747]], ['lapse restarts as new business', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[81917, False], [None, False], [245751, False]]}, [81917, None, 245751]], ['within caps', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[82917, False], [80917, False]]}, [82917, 80917]], ['mixed history', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[92584, False], [202024, False], [62931, True], [150823, False]]}, [91747, 102757, 62931, 70483]]], [['large increase phased in', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[280726, False], [280726, False], [280726, False]]}, [158610, 179229, 202529]], ['large decrease capped', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[70181, False], [70181, False]]}, [133345, 126678]], ['coverage change exempt then capped', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[280726, True], [421089, False]]}, [280726, 317220]], ['new business exempt', {'prior': 0, 'up': 130, 'down': 50, 'years': [[140363, False], [280726, False]]}, [140363, 158610]], ['lapse restarts as new business', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[140363, False], [None, False], [421089, False]]}, [140363, None, 421089]], ['within caps', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[141363, False], [139363, False]]}, [141363, 139363]], ['mixed history', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[224001, True], [54488, False], [53043, False], [82834, False]]}, [224001, 212801, 202161, 192053]]], [['large increase phased in', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[262850, False], [262850, False], [262850, False]]}, [149825, 170801, 194713]], ['large decrease capped', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[65712, False], [65712, False]]}, [124854, 118611]], ['coverage change exempt then capped', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[262850, True], [394275, False]]}, [262850, 299649]], ['new business exempt', {'prior': 0, 'up': 140, 'down': 50, 'years': [[131425, False], [262850, False]]}, [131425, 149825]], ['lapse restarts as new business', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[131425, False], [None, False], [394275, False]]}, [131425, None, 394275]], ['within caps', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[132425, False], [130425, False]]}, [132425, 130425]], ['mixed history', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[105255, True], [201448, True], [175992, True], [84220, False]]}, [105255, 201448, 175992, 167192]]], [['large increase phased in', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[258006, False], [258006, False], [258006, False]]}, [148353, 170606, 196197]], ['large decrease capped', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[64501, False], [64501, False]]}, [122553, 116425]], ['coverage change exempt then capped', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[258006, True], [387009, False]]}, [258006, 296707]], ['new business exempt', {'prior': 0, 'up': 150, 'down': 50, 'years': [[129003, False], [258006, False]]}, [129003, 148353]], ['lapse restarts as new business', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[129003, False], [None, False], [387009, False]]}, [129003, None, 387009]], ['within caps', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[130003, False], [128003, False]]}, [130003, 128003]], ['mixed history', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[151965, False], [114334, False], [235286, False], [180318, True]]}, [148353, 140935, 162075, 180318]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), 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 fixture	Actual	Expected	Outcome
large increase phased in	`[282332, 282332, 282332]`	`[156694, 173930, 193062]`	Failed
large decrease capped	`[134108, 127403]`	`[134108, 127403]`	Passed
coverage change exempt then capped	`[282332, 423498]`	`[282332, 313389]`	Failed
new business exempt	`[141166, 282332]`	`[141166, 156694]`	Failed
lapse restarts as new business	`[141166, None, 423498]`	`[141166, None, 423498]`	Passed
within caps	`[142166, 140166]`	`[142166, 140166]`	Passed
mixed history	`[172018, 166564, 197332, 213340]`	`[156694, 166564, 184886, 205223]`	Failed

SHA-256 / 857342d86f133b72b06b3086f10f3e5caad639dd80c9372f9d9ac22d182e3475

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(x):
    prev=x['prior']; out=[]
    for ind,changed in x['years']:
        if ind is None:
            out.append(None); prev=0; continue
        if changed or prev==0:
            cur=ind
        else:
            hi=math.floor(Fraction((prev+ind)//2*(1000+x['up']),1000)+Fraction(1,2))
            lo=math.floor(Fraction(prev*(1000-x['down']),1000)+Fraction(1,2))
            cur=max(lo,min(hi,ind))
        out.append(cur); prev=cur
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['large increase phased in', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[282332, False], [282332, False], [282332, False]]}, [156694, 173930, 193062]], ['large decrease capped', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[70583, False], [70583, False]]}, [134108, 127403]], ['coverage change exempt then capped', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[282332, True], [423498, False]]}, [282332, 313389]], ['new business exempt', {'prior': 0, 'up': 110, 'down': 50, 'years': [[141166, False], [282332, False]]}, [141166, 156694]], ['lapse restarts as new business', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[141166, False], [None, False], [423498, False]]}, [141166, None, 423498]], ['within caps', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[142166, False], [140166, False]]}, [142166, 140166]], ['mixed history', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[172018, False], [166564, False], [197332, False], [213340, False]]}, [156694, 166564, 184886, 205223]]], [['large increase phased in', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[163834, False], [163834, False], [163834, False]]}, [91747, 102757, 115088]], ['large decrease capped', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[40958, False], [40958, False]]}, [77821, 73930]], ['coverage change exempt then capped', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[163834, True], [245751, False]]}, [163834, 183494]], ['new business exempt', {'prior': 0, 'up': 120, 'down': 50, 'years': [[81917, False], [163834, False]]}, [81917, 91747]], ['lapse restarts as new business', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[81917, False], [None, False], [245751, False]]}, [81917, None, 245751]], ['within caps', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[82917, False], [80917, False]]}, [82917, 80917]], ['mixed history', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[92584, False], [202024, False], [62931, True], [150823, False]]}, [91747, 102757, 62931, 70483]]], [['large increase phased in', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[280726, False], [280726, False], [280726, False]]}, [158610, 179229, 202529]], ['large decrease capped', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[70181, False], [70181, False]]}, [133345, 126678]], ['coverage change exempt then capped', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[280726, True], [421089, False]]}, [280726, 317220]], ['new business exempt', {'prior': 0, 'up': 130, 'down': 50, 'years': [[140363, False], [280726, False]]}, [140363, 158610]], ['lapse restarts as new business', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[140363, False], [None, False], [421089, False]]}, [140363, None, 421089]], ['within caps', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[141363, False], [139363, False]]}, [141363, 139363]], ['mixed history', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[224001, True], [54488, False], [53043, False], [82834, False]]}, [224001, 212801, 202161, 192053]]], [['large increase phased in', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[262850, False], [262850, False], [262850, False]]}, [149825, 170801, 194713]], ['large decrease capped', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[65712, False], [65712, False]]}, [124854, 118611]], ['coverage change exempt then capped', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[262850, True], [394275, False]]}, [262850, 299649]], ['new business exempt', {'prior': 0, 'up': 140, 'down': 50, 'years': [[131425, False], [262850, False]]}, [131425, 149825]], ['lapse restarts as new business', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[131425, False], [None, False], [394275, False]]}, [131425, None, 394275]], ['within caps', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[132425, False], [130425, False]]}, [132425, 130425]], ['mixed history', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[105255, True], [201448, True], [175992, True], [84220, False]]}, [105255, 201448, 175992, 167192]]], [['large increase phased in', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[258006, False], [258006, False], [258006, False]]}, [148353, 170606, 196197]], ['large decrease capped', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[64501, False], [64501, False]]}, [122553, 116425]], ['coverage change exempt then capped', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[258006, True], [387009, False]]}, [258006, 296707]], ['new business exempt', {'prior': 0, 'up': 150, 'down': 50, 'years': [[129003, False], [258006, False]]}, [129003, 148353]], ['lapse restarts as new business', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[129003, False], [None, False], [387009, False]]}, [129003, None, 387009]], ['within caps', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[130003, False], [128003, False]]}, [130003, 128003]], ['mixed history', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[151965, False], [114334, False], [235286, False], [180318, True]]}, [148353, 140935, 162075, 180318]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), 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 fixture	Actual	Expected	Outcome
large increase phased in	`[235041, 282332, 282332]`	`[156694, 173930, 193062]`	Failed
large decrease capped	`[134108, 127403]`	`[134108, 127403]`	Passed
coverage change exempt then capped	`[282332, 391736]`	`[282332, 313389]`	Failed
new business exempt	`[141166, 235041]`	`[141166, 156694]`	Failed
lapse restarts as new business	`[141166, None, 423498]`	`[141166, None, 423498]`	Passed
within caps	`[142166, 140166]`	`[142166, 140166]`	Passed
mixed history	`[172018, 166564, 197332, 213340]`	`[156694, 166564, 184886, 205223]`	Failed

SHA-256 / 7e2430d18b722baaf99f6c316303f107b83531726e8ce6b8a8ce113204c53890

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
from fractions import Fraction
N = 1
observations = []
def solve(x):
    prev=x['prior']; out=[]
    for ind,changed in x['years']:
        if ind is None:
            out.append(None); prev=0; continue
        if changed or prev==0:
            cur=ind
        else:
            hi=math.floor(Fraction(prev*(1000+x['up']),1000)+Fraction(1,2))
            lo=math.floor(Fraction(prev*(1000-x['down']),1000)+Fraction(1,2))
            cur=max(lo,min(hi,ind))
        out.append(cur); prev=cur
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['large increase phased in', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[282332, False], [282332, False], [282332, False]]}, [156694, 173930, 193062]], ['large decrease capped', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[70583, False], [70583, False]]}, [134108, 127403]], ['coverage change exempt then capped', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[282332, True], [423498, False]]}, [282332, 313389]], ['new business exempt', {'prior': 0, 'up': 110, 'down': 50, 'years': [[141166, False], [282332, False]]}, [141166, 156694]], ['lapse restarts as new business', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[141166, False], [None, False], [423498, False]]}, [141166, None, 423498]], ['within caps', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[142166, False], [140166, False]]}, [142166, 140166]], ['mixed history', {'prior': 141166, 'up': 110, 'down': 50, 'years': [[172018, False], [166564, False], [197332, False], [213340, False]]}, [156694, 166564, 184886, 205223]]], [['large increase phased in', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[163834, False], [163834, False], [163834, False]]}, [91747, 102757, 115088]], ['large decrease capped', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[40958, False], [40958, False]]}, [77821, 73930]], ['coverage change exempt then capped', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[163834, True], [245751, False]]}, [163834, 183494]], ['new business exempt', {'prior': 0, 'up': 120, 'down': 50, 'years': [[81917, False], [163834, False]]}, [81917, 91747]], ['lapse restarts as new business', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[81917, False], [None, False], [245751, False]]}, [81917, None, 245751]], ['within caps', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[82917, False], [80917, False]]}, [82917, 80917]], ['mixed history', {'prior': 81917, 'up': 120, 'down': 50, 'years': [[92584, False], [202024, False], [62931, True], [150823, False]]}, [91747, 102757, 62931, 70483]]], [['large increase phased in', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[280726, False], [280726, False], [280726, False]]}, [158610, 179229, 202529]], ['large decrease capped', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[70181, False], [70181, False]]}, [133345, 126678]], ['coverage change exempt then capped', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[280726, True], [421089, False]]}, [280726, 317220]], ['new business exempt', {'prior': 0, 'up': 130, 'down': 50, 'years': [[140363, False], [280726, False]]}, [140363, 158610]], ['lapse restarts as new business', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[140363, False], [None, False], [421089, False]]}, [140363, None, 421089]], ['within caps', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[141363, False], [139363, False]]}, [141363, 139363]], ['mixed history', {'prior': 140363, 'up': 130, 'down': 50, 'years': [[224001, True], [54488, False], [53043, False], [82834, False]]}, [224001, 212801, 202161, 192053]]], [['large increase phased in', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[262850, False], [262850, False], [262850, False]]}, [149825, 170801, 194713]], ['large decrease capped', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[65712, False], [65712, False]]}, [124854, 118611]], ['coverage change exempt then capped', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[262850, True], [394275, False]]}, [262850, 299649]], ['new business exempt', {'prior': 0, 'up': 140, 'down': 50, 'years': [[131425, False], [262850, False]]}, [131425, 149825]], ['lapse restarts as new business', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[131425, False], [None, False], [394275, False]]}, [131425, None, 394275]], ['within caps', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[132425, False], [130425, False]]}, [132425, 130425]], ['mixed history', {'prior': 131425, 'up': 140, 'down': 50, 'years': [[105255, True], [201448, True], [175992, True], [84220, False]]}, [105255, 201448, 175992, 167192]]], [['large increase phased in', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[258006, False], [258006, False], [258006, False]]}, [148353, 170606, 196197]], ['large decrease capped', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[64501, False], [64501, False]]}, [122553, 116425]], ['coverage change exempt then capped', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[258006, True], [387009, False]]}, [258006, 296707]], ['new business exempt', {'prior': 0, 'up': 150, 'down': 50, 'years': [[129003, False], [258006, False]]}, [129003, 148353]], ['lapse restarts as new business', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[129003, False], [None, False], [387009, False]]}, [129003, None, 387009]], ['within caps', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[130003, False], [128003, False]]}, [130003, 128003]], ['mixed history', {'prior': 129003, 'up': 150, 'down': 50, 'years': [[151965, False], [114334, False], [235286, False], [180318, True]]}, [148353, 140935, 162075, 180318]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(args), 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 fixture	Actual	Expected	Outcome
large increase phased in	`[156694, 173930, 193062]`	`[156694, 173930, 193062]`	Passed
large decrease capped	`[134108, 127403]`	`[134108, 127403]`	Passed
coverage change exempt then capped	`[282332, 313389]`	`[282332, 313389]`	Passed
new business exempt	`[141166, 156694]`	`[141166, 156694]`	Passed
lapse restarts as new business	`[141166, None, 423498]`	`[141166, None, 423498]`	Passed
within caps	`[142166, 140166]`	`[142166, 140166]`	Passed
mixed history	`[156694, 166564, 184886, 205223]`	`[156694, 166564, 184886, 205223]`	Passed

SHA-256 / 3b7ed4a5cf329dca950fa1e9a102df9ee087ce76d5c04043d0e19f9503014a67

Verification & scope

A deterministic bounded teaching model of a stipulated toy rating contract. Amounts are integer cents and factors exact rationals; it makes no claim of conformance with any filed rating plan, bureau manual or jurisdiction. 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 2026-09-29T14:47:13.004639+00:00.

Case digest / 2405ab90ef7eeb1793574a42f17281339ec7a13728fbc078b94712a5b1e38a92