A proration calculator with three modes for different jobs. (1) Split by ratio: enter a total and a weight for each item (e.g. 3:2:1) and it allocates the total in proportion — remainders are distributed with the largest-remainder method so the allocated amounts add up to the total exactly (good for cost allocation across departments, shared expenses, or shares). (2) By % (home-office): enter an amount and a business-use percentage for each expense row (rent, electricity, internet, …) to see the business portion and the private portion per row and in total. (3) Daily / pro rata: enter a full-period amount with the days used and days in the period to get the pro-rated amount; tick the calendar-month option to fill in that month's day count (28–31) automatically — handy for prorating rent or a monthly fee on move-in/move-out. You can pick the rounding unit (1/10/100/1000). Amounts are never uploaded — everything is calculated in your browser. This tool only helps with the arithmetic of proration; it does not give tax or accounting advice.
How to use
- Pick a mode at the top: Split by ratio, By % (home-office), or Daily / pro rata.
- For ratio, enter the total and a weight per row; for %, enter an amount and use-% per row.
- Results update instantly (ratio mode balances remainders so the sum matches the total exactly).
FAQ
Will the allocated amounts add up to the total exactly?
Yes in "Split by ratio" mode. It uses the largest-remainder method, so the allocated amounts always sum to the total. Leftover units from rounding are added to the rows with the largest fractional shares first.
Can I use it for home-office (business-use) expenses?
Yes. In "By % (home-office)" mode, enter an amount and a business-use percentage for each row (rent, electricity, internet, …) and it shows the business and private portions per row and as a total. Whether an expense is deductible and at what rate is up to you or your accountant — this tool only does the arithmetic.
Can I prorate rent or a monthly fee by days?
Yes. In "Daily / pro rata" mode, enter the full-period amount, the days used and the days in the period to get the pro-rated amount. Tick "Use a calendar month" and pick a month to fill in that month's day count automatically. It also shows the per-day amount and the remainder.
Are the amounts I enter stored or uploaded?
Amounts and labels are never sent to a server and are not saved. Everything is calculated in your browser (only the mode and rounding unit are stored on your device for next time, and can be cleared with Reset).