Proportional Allocation Calculator
Enter a total amount and the values to split it by, and the calculator allocates the amount in proportion. The shares can be adjusted so that they add up exactly to the total, down to the cent.
How the allocation works
The amount is divided in proportion to the values:
- Amount of a row = total × the row's value ÷ the sum of the values
A value can be anything you are splitting by: an area, a headcount, sales, a number of days. A ratio such as 3 : 2 : 1 and real values such as 60, 40 and 20 give the same result. The currency does not matter, and none is assumed.
Handling the leftover cents (two methods)
An allocation usually does not come out to a whole number of cents. You can choose between two methods.
Make the shares add up to the total (default; largest remainder method)
- Work out each amount and round it down to the cent.
- Subtract the sum from the total to find the leftover cents.
- Give the leftover one cent at a time to the rows with the largest fractions (the part below a cent), largest first.
- Rows with equal fractions go in the order you entered them (the upper row first).
The shares always add up exactly to the total. Because ties are broken by the order of the rows, the order you enter them in can change which row receives an extra cent.
Only round each row
Each row is rounded to the cent with the method you choose (round down, round half up or round up). The sum can be a little off from the total, so the calculator shows the sum and the difference.
Example
An amount of 1,000.00 is split 3 : 2 : 1 (the exact shares are 500.00, 333.33… and 166.66…).
| Method | Shares | Sum | Difference |
|---|---|---|---|
| Make the shares add up to the total | 500.00 · 333.33 · 166.67 | 1,000.00 | 0.00 |
| Round down only | 500.00 · 333.33 · 166.66 | 999.99 | −0.01 |
| Round half up only | 500.00 · 333.33 · 166.67 | 1,000.00 | 0.00 |
| Round up only | 500.00 · 333.34 · 166.67 | 1,000.01 | +0.01 |
With "make the shares add up to the total", rounding down leaves one cent over, and it goes to the third row, which has the largest fraction (166.66…).
Notes
- The amount to allocate can be 0 or more, up to 9,999,999,999.99, with up to 2 decimal places. The calculation is done in whole cents (or the smallest unit of your currency), so there is no floating-point error.
- Each value is a number of 0 or more with up to 9 digits before the decimal point and 6 decimal places. A row with a value of 0 receives 0. If all the values are 0, the amount cannot be allocated.
- There are 2 to 20 rows. Rows with no value are not counted (at least 2 rows with a value are needed).
- If accounting or tax rules fix how fractions must be handled, choose the method that matches those rules.
- To find a percentage, see the Percentage Calculator. To divide a bill, see the Split Bill Calculator. To work out a share of a cost breakdown, see the Cost Breakdown Calculator.
Frequently asked questions
My shares don't add up to the total. What should I do?
Choose "Make the shares add up to the total". The leftover cents are given out to the rows with the largest fractions.
Which row gets the extra cent when the fractions are equal?
The upper row, in the order you entered the rows.
How do I split a cost by area or headcount?
Enter the area or headcount of each row as its value. You do not need to turn them into ratios.
Can I allocate amounts with cents?
Yes. You can enter up to 2 decimal places, in any currency that works in hundredths.