Proration
Partial months are billed by day, automatically, in both directions.
A resident who occupies a room for part of a month is billed for that part, by day ratio. It happens automatically at both ends of a tenancy, and it recalculates when a date changes — moving a move-out date later restores the fuller month, moving it earlier trims it.
How the amount is worked out
The ratio is days occupied ÷ days in that period. February and August therefore give different answers for the same number of days, which is intended: a day in a 28-day month is worth more than a day in a 31-day one.
Two details decide whether the numbers reconcile:
- Each component is prorated separately, then summed. Rent, the utility fee, building maintenance, surcharges and any catalogue fees are each scaled and rounded on their own. The invoice total is the sum of those rounded parts — not the monthly total scaled once.
- A full month is never prorated at all. When the occupied days equal the period's days the exact rates are used, with no ratio and no rounding, so a normal month can never drift by a yen.
Point 1 is why a prorated invoice can differ by one yen from "monthly total × ratio" done on a calculator. A one-day slice of a ¥102,000 month sums to ¥3,291 across its components but rounds to ¥3,290 as a single figure. The itemised figure is the correct one, because it is the one that matches the lines the resident is actually billed for.
Discounts inside a prorated period
A discount is clipped to the part of the window that overlaps the period, and that clipped slice is used as-is. It is not re-scaled by the period's day ratio a second time — doing both would shrink the discount twice.
The first month and the last month
These two look different from every other month, and both differences are normal:
- The first month may not appear as rent at all. It is commonly folded into the move-in invoice instead, together with the deposit and the one-off fees. Looking for a rent entry that month and not finding one is not a missing charge.
- The last month is prorated to the move-out date, and recalculates if that date moves. A date change is the supported way to change the amount.
The rule that matters
Never hand-edit an amount to simulate proration. The calculated figure is what reconciles against payments and against the ledger's own lines. A typed-over number looks right until the month it does not, and by then the reservation, the invoice and the payment disagree with each other and nobody can tell which was intended.
If the amount is wrong, the date is wrong, or a fee rule is wrong. Fix whichever it is and let the figure recalculate.
Where it shows up
Prorated periods appear as their own lines on the move-in invoice, each stamped with the month it belongs to, so a stay that straddles a month boundary reports into both months rather than landing entirely in one. See The ledger for how those per-line periods work, and Contract dates for which date drives which end.