Mid-Month Rent Change Calculator
Amounts are in USD. Calculations stay in your browser.
Enter the rental details, then select Calculate.
Accounting breakdown
| Detail | Current rent | New rent |
|---|---|---|
| Rent period | - | - |
| Monthly rent | - | - |
| Calculation | - | - |
| Prorated amount | - | - |
30-day accounting month:
Disclaimer: This calculator is provided for general informational purposes only. Verify lease terms, day-count conventions, local requirements, and all figures before charging or paying prorated rent.
How it's calculated
When rent changes partway through a month, the month is split in two. The current rent applies through the day before the change. The new rent applies from the change date to the end of the month.
Each part = monthly rent × days in that part ÷ days in the month
Each part is rounded to the nearest cent (half a cent rounds up), and the two parts are added together. This way, the amounts in the breakdown always add up exactly to the total.
Example: new rent starts July 16
Rent goes from $1,800 to $1,875 on July 16, 2026.
- July 1–15 at current rent: $1,800 × 15 ÷ 31 = $870.97
- July 16–31 at new rent: $1,875 × 16 ÷ 31 = $967.74
- Total with actual days in month: $1,838.71
With a 30-day accounting month, each rent gets 15 days: $900.00 + $937.50 = $1,837.50.
Actual days vs. 30-day accounting month
Use whichever method your lease or company policy specifies. If neither says, settle it before you bill, because the two methods can produce noticeably different amounts.
The 30-day method gives the current rent one day for each day before the change, and the new rent the rest of the 30. A change on the 31st is treated as day 30, so the new rent gets 1 day. February is still divided by 30. A change on February 28, 2026 gives the current rent 27 days and the new rent 3 days, even though only one calendar day is at the new rent. The result explains when this happens and shows the actual-days total for comparison.
Common questions
Which rent applies on the change date?
The new rent.
What if the new rent starts on the 1st?
Nothing is split. The full new rent is due for that month.
Why is my spreadsheet a cent off?
The calculator rounds each part before adding them, so the breakdown matches the total. Rounding only the combined amount can differ by one cent.