Earned Premium Calculation in Reinsurance: Methods Explained
On this page
- Earned Premium Calculation in Reinsurance: Removing Spreadsheet Errors From Treaty Earnings
- Key Takeaways
- What Is Earned Premium in Reinsurance?
- Which Earning Methods Do Reinsurers Use?
- How Do Risks-Attaching and Losses-Occurring Treaties Earn?
- What Does a Worked Example Show?
- What Data Does the Calculation Need?
- Which Spreadsheet Errors Distort Treaty Earnings?
- How Do You Calculate Earned Premium Step by Step?
- How Does Earning Interact With Financial Reporting?
- Where Does Automation Help?
- Which Metrics Show Earnings Are Under Control?
- What Should CFOs and Chief Actuaries Do Next?
- Key Terms
- Sources
- Frequently Asked Questions
Earned Premium Calculation in Reinsurance: Removing Spreadsheet Errors From Treaty Earnings
Last reviewed: November 2026
A quota share can be priced perfectly and still report the wrong result for a year. If its premium is earned on the wrong pattern, half the income lands in the wrong period.
Short answer: Earned premium calculation in reinsurance apportions premium over the period when cover is actually provided. The method, such as daily pro rata or 1/24ths, matters less than applying it to the right basis: losses-occurring or risks-attaching.
Key Takeaways
- Basis comes before method. Risks-attaching and losses-occurring treaties earn over different periods.
- Risks-attaching often means 24 months. A one-year treaty on annual policies can earn into a second year.
- 1/24ths is an approximation. It assumes mid-month inception, which misstates business written on the first.
- Reconcile every period. Written premium should equal earned premium plus the change in unearned premium.
What Is Earned Premium in Reinsurance?
Earned premium in reinsurance is the part of the reinsurance premium that relates to cover already provided. The Reinsurance Association of America defines it by the expired portion of the policies reinsured.
The rest is unearned premium. It sits on the balance sheet until the cover it pays for has run.
Which Earning Methods Do Reinsurers Use?
Reinsurers mostly use time apportionment, either exact or approximate. HMRC's general insurance guidance says time apportionment applies unless there is marked unevenness in the incidence of risk.
| Method | How it works | Best used when |
|---|---|---|
| Daily pro rata (365ths) | Earns by exact days elapsed | Inception dates are known |
| 1/24ths | Assumes each month's business starts mid-month | Data is monthly, such as bordereaux |
| 1/8ths | Assumes each quarter's business starts mid-quarter | Data is only quarterly |
| Risk profile | Earns in line with expected risk | Risk is seasonal or uneven |
Approximations are not wrong. They become wrong when their assumption does not fit the business.
HMRC's worked example shows the effect. On the same four contracts, the 24ths method gives an unearned provision of 698 against 656 on the 365ths method.
How Do Risks-Attaching and Losses-Occurring Treaties Earn?
Losses-occurring treaties earn over the treaty period, while risks-attaching treaties earn over the underlying policies' terms. This is the most important choice in the calculation.
How does a losses-occurring treaty earn?
A losses-occurring treaty covers losses that happen during the treaty period, whatever the policy's inception date. Its premium usually earns over that period, evenly unless risk is seasonal.
How does a risks-attaching treaty earn?
A risks-attaching treaty covers policies written during the treaty period, for their full term. A policy written on the treaty's last day stays covered for another year.
So a one-year risks-attaching treaty on annual policies is exposed for up to 24 months. Its premium should earn over that longer pattern, following the underlying business.
What Does a Worked Example Show?
These illustrative examples show how basis and method change the answer. All figures are invented for the example.
How is premium earned on a losses-occurring excess of loss treaty?
An annual losses-occurring treaty runs from 1 January to 31 December 2026, with premium of 1,200,000. At 30 June, 181 of 365 days have elapsed.
Daily pro rata earns 181/365 × 1,200,000 = 595,068. Simple monthly earning gives 600,000, a small difference on an evenly earned cover.
How is premium earned on a risks-attaching quota share?
A one-year risks-attaching quota share starts on 1 January 2026. The cedent writes annual policies evenly, ceding 1,000,000 of premium each month, so 12,000,000 in total.
Using 1/24ths, January's cessions are 23/24 earned by 31 December, February's 21/24, and so on to December's 1/24. The total is 144/24 × 1,000,000 = 6,000,000.
| Approach at 31 December 2026 | Earned | Unearned |
|---|---|---|
| Correct: follow underlying policies (1/24ths) | 6,000,000 | 6,000,000 |
| Wrong: earn over treaty period | 12,000,000 | 0 |
The wrong approach brings 6,000,000 of premium forward into 2026. It also leaves no unearned premium for cover that runs well into 2027.
When does the 1/24ths method mislead?
An annual cover incepts on 1 January with premium of 1,200,000. At 31 March, daily pro rata earns 90/365, or 295,890.
The 1/24ths method assumes a 15 January start and earns 5/24, or 250,000. The gap exists because the method expects mid-month inception, while this business started on the first.
For a book concentrated on 1 January renewals, that lag repeats at every quarter end. It reverses by expiry, but it shifts reported results between periods.
What Data Does the Calculation Need?
The calculation needs the treaty basis, the premium by period of writing, and the term of the underlying policies. Without the writing pattern, any earning method is a guess.
Policy terms deserve a closer look. A risks-attaching treaty on multi-year engineering or construction policies can stay exposed far longer than 24 months.
Ask cedents for premium by month of inception and by policy term where it matters. That one bordereau field often fixes more errors than any formula change.
How should additional premiums be earned?
Adjustment and reinstatement premiums need their own documented earning rule. Practice differs between frameworks, so the key control is a written policy applied consistently and agreed with auditors.
Which Spreadsheet Errors Distort Treaty Earnings?
The errors that distort treaty earnings most are basis errors and hard-coded assumptions. They are rarely visible in a summary total.
| Error | Effect | Fix |
|---|---|---|
| Risks-attaching earned over treaty period | Earnings brought forward | Earn with the underlying policies |
| 1/24ths on first-of-month business | Earnings lag by about half a month | Use daily pro rata where dates are known |
| 365 days hard-coded | Small errors in leap years, such as 2028 | Use actual days in the period |
| Seasonal risk earned evenly | Profit shown in the wrong quarter | Use a documented risk profile |
| Adjustments with no earning rule | Inconsistent treatment each period | Document a policy for each premium type |
| Cut-off termination ignored | Unearned premium overstated | Reflect returned unearned premium |
The last row depends on the wording. Under a cut-off clause, the RAA notes that unearned premium is returned to the ceding company.
How Do You Calculate Earned Premium Step by Step?
You calculate earned premium by fixing the basis, choosing a method that fits the data, and reconciling every period. The process has six steps.
- Confirm the basis. Read whether the treaty is losses-occurring or risks-attaching, and how termination works.
- Identify the exposure period. Use the treaty period, or the underlying policy terms for risks-attaching cover.
- Choose the method. Use daily pro rata where inception dates are known, and approximations only where data requires.
- Check the risk profile. Apply a profile where risk is markedly uneven, and document why.
- Calculate at the finest level available. Earn by month of writing or by policy, not on annual totals.
- Reconcile. Confirm that written premium equals earned premium plus the change in unearned premium.
Step five removes most errors in one move. Annual totals hide the writing pattern that drives the result.
Earnings feed directly into the close. Our guide to the reinsurance quarterly close shows how late earned premium figures become estimates.
How Does Earning Interact With Financial Reporting?
The earning pattern should reflect when cover is provided, whatever accounting framework applies. Your accounting policy then decides how that pattern feeds revenue and liabilities.
For reinsurers reporting under IFRS 17, earning assumptions connect to wider measurement choices. See our guide to the IFRS 17 loss recovery component for one related area.
Treaty structure also shapes the pattern. Our explainer on proportional vs non-proportional reinsurance covers how each type cedes premium.
Where Does Automation Help?
Automation helps by calculating from structured treaty terms rather than spreadsheet formulas copied between files. It does not choose the earning method or the risk profile.
Reinsurance treaty management software holds treaty terms, premium calculation and calculation rules as structured, versioned data, with calculation history and an audit trail. That gives earned premium work a single, traceable source for basis, dates and premium.
Actuaries and finance teams still own the method. They decide which pattern fits, and they sign off the result.
Which Metrics Show Earnings Are Under Control?
The best metrics show whether earnings reconcile and whether assumptions are documented. Review them each quarter.
| Metric | What it tells you |
|---|---|
| Written vs earned plus change in unearned | Whether the calculation reconciles |
| Treaties with documented basis and method | Whether assumptions are visible |
| Prior-period earning corrections | Whether errors reach reported results |
| Treaties earned on annual totals | Where precision can improve |
What Should CFOs and Chief Actuaries Do Next?
CFOs and chief actuaries should check the basis and method for their largest treaties first. A short review usually finds the biggest exposure to error.
- List every risks-attaching treaty and confirm it earns with the underlying policies.
- Replace 1/24ths with daily pro rata where inception dates are known.
- Document a risk profile for seasonal covers, with the reason.
- Add the written-earned-unearned reconciliation to the quarterly close.
Key Terms
- Earned premium: Premium relating to the expired portion of cover.
- Unearned premium: Premium relating to the unexpired portion of cover, held on the balance sheet.
- Losses occurring during (LOD): Cover for losses that happen during the treaty period.
- Risks attaching during (RAD): Cover for policies written during the treaty period, for their full term.
- 1/24ths method: An earning approximation that assumes mid-month inception for each month's business.
- Cut-off: A termination basis under which the reinsurer stops covering later losses and returns unearned premium.
Sources
- HMRC General Insurance Manual: GIM2100 Unearned Premium Provision
- HMRC General Insurance Manual: GIM2110 UPP worked example
- Reinsurance Association of America: Glossary of Reinsurance Terms
- Insurnest: Reinsurance Treaty Management
Frequently Asked Questions
How is earned premium calculated in reinsurance?
Earned premium in reinsurance is calculated by apportioning the reinsurance premium over the period in which cover is provided. Most reinsurers use daily pro rata or an approximation such as the 1/24ths method, applied to the treaty period for losses-occurring covers or to the underlying policies for risks-attaching covers.
What is the difference between earned and unearned reinsurance premium?
Earned reinsurance premium relates to the expired portion of cover, while unearned reinsurance premium relates to the unexpired portion. Written premium equals earned premium plus the change in unearned premium, which gives finance teams a simple reconciliation check every period.
What is the 1/24ths method?
The 1/24ths method is an approximation that assumes contracts incepting in a month start evenly through that month, so on average at mid-month. For a 31 December year end, annual premiums written in January are 1/24th unearned, February premiums 3/24ths unearned, and so on.
How does a risks-attaching treaty earn premium?
A risks-attaching treaty earns premium in line with the underlying policies it covers, because it covers policies written during the treaty period for their full term. For annual policies written evenly through a one-year treaty, earning spreads over about 24 months, with roughly half earned by the treaty's expiry.
How does a losses-occurring treaty earn premium?
A losses-occurring treaty earns premium over the treaty period, because it covers losses that happen during that period regardless of when the underlying policies were written. An annual losses-occurring treaty usually earns evenly over its 12 months unless the risk is seasonal.
When should earned premium follow a risk profile instead of time?
Earned premium should follow a risk profile instead of straight time apportionment when risk is markedly uneven over the cover period. Seasonal perils such as windstorm, or covers with risk concentrated at specific times, are typical cases where a profile-based earning pattern is more accurate.
Why does the 1/24ths method misstate business incepting on the first of the month?
The 1/24ths method misstates business incepting on the first of the month because it assumes mid-month inception. For an annual cover incepting on 1 January, it earns about half a month less by each period end than daily pro rata, which matters for large treaty renewals.
What are common spreadsheet errors in reinsurance earned premium?
Common spreadsheet errors in reinsurance earned premium include earning a risks-attaching treaty over the treaty period, applying 1/24ths to business that incepts on one date, hard-coding 365 days in leap years, and earning additional premiums with no documented policy.
Hitul Mistry
CEO, Insurnest
An InsurTech leader with more than a decade of experience across insurance and technology, focused on solving business problems with the help of technology. Has worked with brokers, insurance carriers, and reinsurance firms across the India, UAE, and US markets.
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