Pro rata insurance calculator.
Direct answer. Enter the policy dates, transaction date, and premium to estimate earned and return premium. You can also estimate a midterm endorsement or apply a carrier-supplied short-rate retention percentage. The calculator uses actual calendar days and keeps every value in your browser.
Premium estimate
Choose the calculation, enter the controlling policy values, and print the result as a workpaper.
How the day-based estimate works.
Pro rata means allocating the proratable policy-term premium in proportion to time. This calculator counts the effective date as the first covered day and treats the expiration date as the first uncovered day. The transaction date divides elapsed days from remaining days.
Return premium = policy-term premium - earned premium
This convention produces 365 days for a January 1, 2026 to January 1, 2027 term and 366 days for a January 1, 2024 to January 1, 2025 term. Some carrier systems use their own calendar, monthly, or rounding conventions, so compare the workpaper with the carrier result.
Choose the one that matches the transaction.
| Mode | Use it for | Important limit |
|---|---|---|
| Pro rata | Time-based cancellation estimates when no different earning rule applies. | Does not apply minimum earned premium, fees, taxes, or a short-rate table. |
| Endorsement | Estimating the remaining-term share of a difference between old and revised full-term premium. | The revised full-term premium must come from an authorized rating source. |
| Short rate | Illustrating the result when a carrier or policy specifies a retention percentage against the otherwise pro-rata return. | There is no universal short-rate percentage. Obtain the actual factor before using this mode. |
A transparent cancellation estimate.
Assume a $3,650 proratable premium for a January 1, 2026 to January 1, 2027 policy and a July 2, 2026 cancellation date. The 365-day term has 182 elapsed days and 183 remaining days. The estimated earned premium is $1,820 and the estimated pro-rata return is $1,830.
If the controlling carrier material requires a 10 percent retention against that pro-rata return, short-rate retention would be $183 and estimated return premium would be $1,647. That 10 percent is an example only. It is not a default factor and should never replace the carrier's actual table, policy provision, or cancellation worksheet.