Prorated Invoice Calculator
Calculate a simple daily proration for a partial subscription, retainer, rent period, or recurring service.
Formula: Daily rate = full-period amount / days in period. Prorated amount = daily rate x billable days.
Free · private in your browser · no signup
Enter the numbers
Calculated result
Daily rate
$30.00
$900.00 divided by 30 days
Prorated amount
$360.00
12 billable days
Unbilled portion
$540.00
18 days not billed
Formula: Daily rate = full-period amount / days in period. Prorated amount = daily rate x billable days.
Use the result correctly
What the calculation means
This uses straight-line daily proration. Your agreement may use actual calendar days, a fixed 30-day month, usage units, or another method. State the covered dates and calculation on the invoice or credit note.
Useful for
- Bill a partial first month of service
- Calculate an unused subscription credit
- Prorate a retainer after a mid-period start or change
Frequently asked questions
Should monthly proration use 30 days or actual days?
Use the method stated in the agreement. Some businesses use actual calendar days; others use a fixed 30-day convention.
Can this calculate a credit?
Yes. Enter the full-period amount and unused days to calculate the unused portion, then document the adjustment with a credit note when appropriate.
Does this calculator include tax?
No. It calculates the prorated base amount only.
More free calculators
Check the next number before it reaches the customer.