Prorating rent sounds fussy, but every method comes down to the same three moves: turn the monthly rent into a daily rate, count the occupied days, and multiply. Here’s the formula, worked examples you can check by hand, and how to pick the right method for your lease.
The prorated rent formula
$$\text{Prorated rent} = (\text{monthly rent} \div \text{days in month}) \times \text{days occupied}$$
That’s it. The only two decisions that change the result are what you divide by (the month’s real length, or a flat 30) and which days count as occupied.
Worked example: mid-month move-in
Rent is $1,800, you move in on August 21st, and August has 31 days:
- Daily rate: $1,800 ÷ 31 = $58.06
- Days occupied: August 21 through August 31 = 11 days
- Prorated rent: $58.06 × 11 = $638.71
You pay for the days you hold the keys — not the full month.
Worked example: mid-month move-out
Same rent of $1,800, and you move out on September 15th. September has 30 days:
- Daily rate: $1,800 ÷ 30 = $60
- Days occupied: September 1 through September 15 = 15 days
- Prorated rent: $60 × 15 = $900
For the final month you owe $900 instead of $1,800. Our prorated rent calculator does this arithmetic for any date range and breaks the total down month by month.
Which days count as occupied?
The standard convention — and the one this calculator uses — is inclusive counting: both the move-in day and the move-out day count as occupied days. Moving in on the 21st of a 30-day month means 10 billable days (the 21st, 22nd … 30th), not 9.
Some landlords count only nights or exclude the move-out day, which is one day less. Either convention is fine as long as it’s stated in the lease — the disagreement to avoid is the silent one.
The three proration methods
1. Actual days in month
Divide by each month’s real length: 31 in January, 28 in a non-leap February, 30 in April. The daily rate therefore changes slightly from month to month ($58.06 in a 31-day month, $64.29 in February) but always matches the real calendar. This is the most accurate and most common method.
2. Flat 30-day month
Always divide by 30, regardless of the month. The daily rate stays identical all year — $1,800 ÷ 30 = $60 — which makes bookkeeping simple. It runs slightly high in 31-day months and slightly low in February. If you’ve seen the question “should prorated rent use 30 or 31 days?”, this method is the landlord’s answer: always 30.
3. Annual (365-day) rate
Some leases divide the yearly rent (monthly rent × 12) by 365 to get one blended daily rate: ($1,800 × 12) ÷ 365 = $59.18 per day, every day of the year. It’s the smoothest method but the least common in residential leases. If your lease uses it, the flat 30-day method produces the closest result here — but the lease wording governs.
| Method | Daily rate for $1,800 rent | Best for |
|---|---|---|
| Actual days | $58.06 (31-day) / $64.29 (Feb) | Accuracy; the default convention |
| Flat 30 days | $60.00 | One stable rate all year |
| Annual 365 days | $59.18 | Leases that specify it |
Which method should you use?
Whichever your lease specifies — that wording always wins. If the lease is silent, actual days is the most common default because it matches the real calendar. Landlords who prefer predictable bookkeeping often choose the flat 30-day method instead. The difference between methods is usually only a dollar or two per day, but over a full month it can matter, so it’s worth checking before you pay.
Common mistakes when prorating rent
- Using the wrong month’s length. Prorating a move-in on the 29th requires that month’s day count (31, 30, 28), not a generic “30”.
- Off-by-one day counts. Forgetting that both endpoints count turns a 10-day stay into 9.
- Mixing methods mid-range. If a date range spans two months, each month gets its own daily rate under the actual-days method — don’t reuse the first month’s rate.
- Prorating charges that are due in full. Security deposits, pet fees, and parking are typically due in full regardless of the move-in date; only the rent itself prorates.
- Trusting mental math. Even the right formula produces wrong numbers when it’s done in your head during a move. Verify with a rent proration calculator — it takes seconds and gives you a line-by-line statement to compare against your landlord’s figure.