Remaining amount
This is the remainder of the full amount, not a guaranteed refund or credit.
Money and planning
Prorated Cost Calculator
Allocate a full-period cost to selected dates using their share of the actual calendar days.
Full amount and date periods
Prorated amount for selected dates
Ready to calculate a partial-period cost
Check the allocation
Daily rate for reference
Shown to 6 decimal places. The prorated amount uses the exact day fraction, not this displayed rate.
- Full billing period
- Selected period
- Days outside the selected period
All amounts use the currency of your input. Calendar days include weekends and holidays.
Recent calculations keeps the last five calculations in this tab. Copy link or Save inputs file to keep the amount, four dates, and end-date choice. CSV exports results; JSON restores inputs. Anyone with the link or file can read those conditions.
Examples and endpoint choices
January 16 through January 31
310.00 × 16 / 31 = 160.00
Full period: January 1–31, 2027. Selected period: January 16–31. With ends included, 16 of 31 days cost 160.00, leaving 150.00. With the same dates and ends excluded, 15 of 30 days cost 155.00. Both day counts change.
Use the actual days in the period
290.00 × 15 / 29 = 150.00
Full period: February 1–29, 2028. Selected period: February 15–29. Including ends gives 15 of 29 days and 150.00. Excluding both ends gives 14 of 28 days and 145.00. The tool does not replace February with a fixed 30-day month.
Keep the full amount reconciled
0.05 × 1 / 2 → 0.03
Full period: January 1–2, 2027. Select January 1 only, with ends included. Half of 0.05 rounds to 0.03; the remainder is 0.02. Excluding ends makes the same-day selected period empty, so its amount is 0.00 and the remainder is 0.05.
Example buttons replace the amount and dates, keep your end-date choice, and calculate. Save current conditions first if you want to keep them.
Formula and calculation rules
Prorated amount = full-period amount × selected days / full-period days. The full period must contain at least one counted day. Both starts count; the checkbox includes or excludes both ends. Dates use the proleptic Gregorian calendar, years 0001–9999, without times of day or time zones.
The input supports up to 15 digits before the decimal point and 2 after it. The amount is converted to whole cents, multiplied by the exact selected-day count, and divided by the full-period day count. The charge is rounded once to the nearest cent, with halfway values rounding up. The remaining amount is the full amount minus that rounded charge, so the two amounts add back exactly.
The daily rate is shown to 6 decimal places and the day percentage to 2; an approximation mark identifies a rounded display. Neither rounded display feeds the charge. Independently prorating many separate pieces may accumulate cent differences; this tool reconciles one selected period with its complement. See the calculation policy.
This tool uses actual calendar days in the periods you enter. It does not apply fixed 30-day conventions, working-day rules, usage metering, taxes, fees, discounts, rate changes, or contract terms. For comparison, Chargebee's proration documentation describes the term-ratio formula and distinguishes day-based from millisecond-based billing. Its platform-specific billing rules are not reproduced here.
Common questions
Can I use a billing cycle that starts halfway through a month?
Yes. Enter its actual start and end dates and the full amount for that exact cycle. The denominator comes from those dates, including any month or year boundary.
Should a renewal or checkout date be included?
Exclude it when it is the first day outside the charged period. Include an end date when it is the final charged day. The same checkbox applies to both periods. For equivalent coverage, an exclusive end is the day after an inclusive final day.
Why does a one-day selection become zero?
Identical selected start and end dates count as one day with ends included and zero days with ends excluded. An empty full billing period is rejected because it cannot be the denominator.
Is the remaining amount the refund I should receive?
It is only the arithmetic complement of the selected amount. A provider or agreement may apply minimum charges, fees, different day-count rules, or no refund. This calculator does not decide entitlement or issue payments.
Can I save and restore all the conditions?
Yes. Recent calculations, a shared link, or a JSON input file restores the amount, all four dates, and the inclusion rule. Restoration does not calculate automatically. Review the values and select Calculate. Reset clears the amount and dates and includes ends again.