FA-58335 / Double-entry ledger accounting / Member archive

Straight-line depreciation journal: cumulative rounding · case 05

The last months of a schedule carry large rounding catch-up amounts.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

x = {'cost', 'salvage', 'life_months', 'start_month', 'convention': 'full_month'|'mid_month'|'next_month', 'through': last month to post}. Depreciable base = cost - salvage. The first charge month is start_month (start_month + 1 for next_month). Charges use cumulative rounding: target accumulated after the j-th charge month is round(base*j/life) or, for mid_month, round(base*(2j-1)/(2*life)), half-up and capped at base; each month posts target - accumulated. Posting stops after 'through' or once accumulated reaches base. Return {'schedule': [[month, amount]], 'accumulated', 'book_value': cost - accumulated}.

Why this case matters

Ledger software must keep debits equal to credits and apply normal-balance, period and cutoff rules exactly; small sign or boundary slips silently misstate financial statements.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: cumulative rounding	`{"accumulated": 1251, "book_value": 3749, "schedule": [[4, 139], [5, 139], [6, 139], [7, 139], [8, 139], [9, 139], [10, 139], [11, 139], [12, 139]]}`	`{"accumulated": 1250, "book_value": 3750, "schedule": [[4, 139], [5, 139], [6, 139], [7, 139], [8, 138], [9, 139], [10, 139], [11, 139], [12, 139]]}`	Failed

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