Prorate an annual subscription refund

mediumbillingPython

When a subscriber cancels early, the unused portion of the annual fee is refunded proportionally.

Refund equals annualAmount × (12 − monthsUsed) ÷ 12, using integer division (floor).
monthsUsed is clamped to the range 0..12 before computing.
monthsUsed 0 yields the full annualAmount; monthsUsed 12 yields 0.

prorate_refund(annual_amount: int, months_used: int) → int

Where you start

def prorate_refund(annual_amount: int, months_used: int) -> int:

Clamp first, then multiply before dividing.

Reference solution in Python

def prorate_refund(annual_amount: int, months_used: int) -> int:
    m = max(0, min(12, months_used))
    return annual_amount * (12 - m) // 12