How to Calculate Prorated Rent — and Why Three Methods Give Three Answers

Why the flat 30-day month is not neutral

Dividing by 30 is the easiest rule to apply and the one most often written into leases, but a year does not contain twelve thirty-day months. Charged at $50 a day for 365 days, a $1,500 rent collects $18,250 instead of $18,000 — 12.17 months of rent in a twelve-month year, an excess of $250. Applied to a single partial month it is a rounding convenience; applied systematically it is a rent increase nobody agreed to.

The annual method avoids that by construction: rent times twelve divided by 365 gives a daily rate that, multiplied by a full year, returns exactly twelve months' rent. It is the fairest of the three across a whole tenancy, and the only one whose daily rate does not change depending on which month you happen to move in. Its drawback is that it needs a leap-year variant — 366 days instead of 365 drops the same 14 days from $690.41 to $688.52.

February is where the methods diverge most

The shorter the month, the larger the daily rate under the actual-days rule, and February pushes it to the extreme. Fourteen days from 15 February cost $750.00 on actual days, $700.00 on a flat 30-day month and $690.41 on the annual method — a spread of $59.59, which is 7.9 percent, against 3.2 percent for the same fourteen days in October.

That asymmetry is why a lease should name its method rather than leave it to whoever writes the first invoice. It also explains the practical compromise many landlords adopt: prorate at the annual daily rate all year, so the tenant pays the same for a day in February as for a day in July and nobody has to argue about which calendar the month came from.

What else belongs in that first payment

Prorating applies to the rent, and often to the service charges billed alongside it, but not to the deposit — a deposit is a fixed amount tied to the tenancy and not to the days occupied, so it is paid in full whatever date you move in. Check whether the charges are prorated on the same convention as the rent; leases that prorate the rent and round the charges to a whole month are common and worth catching before the first payment leaves.

Keep the arithmetic on paper. A one-line calculation showing the convention, the day count and the daily rate, sent by email before the first payment and acknowledged, costs nothing and settles in advance the only question that a partial month can produce. If the landlord's figure differs, the disagreement is now about a named method rather than about a total, which is a far shorter conversation.

Frequently asked questions

Does the move-in day itself count?

Yes, in the normal case: liability starts on the day the lease starts and you take possession, so from 18 to 31 October inclusive is 14 days. Counting 13 by subtracting the dates is the classic off-by-one, and it is worth roughly one day's rent — $48 to $50 on a $1,500 monthly rent.

Which method should a lease use if it does not say?

There is no universal default, which is precisely the problem. In practice the actual-days rule is the most defensible for a single month because it charges for the month you actually lived in, and the annual method is the most defensible across a whole tenancy because it never collects more than twelve months of rent in a year. Pick one, write it into the lease, and use it at both ends.

Does moving out mid-month work the same way?

The arithmetic is the same, but the day count is not always what you expect: what you owe usually runs to the end of the notice period rather than to the day you hand back the keys, and leaving early does not shorten it. Work out the last chargeable day from the notice rules first, then prorate from there using the same convention as the first month.