Reinsurance Share Calculator

Work out reinsurance share instantly with clear inputs, formula shown and shareable results.

About Reinsurance Share Calculator

Under a surplus treaty the insurer keeps one line — its retention — and cedes the surplus up to a stated number of lines. The retained proportion of every risk written within capacity is retention divided by the sum insured, and claims are shared in the same proportion.

Formulas

Treaty capacity

Capacity = Retention x (1 + Number of lines)

Retained share

Retained % = Retention / Sum insured placed

Claim split

Ceded claim = Claim x (1 - Retained share)

Worked example

With the default values below, Reinsurance Share Calculator returns Share ceded to reinsurers of 90.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total sum insured: 500,000,000
Insurer's retention: 50,000,000
Treaty capacity in lines of retention: 9
Claim amount to allocate: 120,000,000

Results

Share ceded to reinsurers: 90.00%
Total treaty capacity: $500,000,000.00
Claim retained by the insurer: $12,000,000.00
Claim ceded to reinsurers: $108,000,000.00

Step by step

1Values used
2Treaty capacity
3Retained share
4Claim split
5Share ceded to reinsurers= 90.00
6Total treaty capacity= 500,000,000.00
7Claim retained by the insurer= 12,000,000.00
8Claim ceded to reinsurers= 108,000,000.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Indicative estimate only. Fees, entitlements, limits and formulas vary by jurisdiction, statute, policy wording and the facts of the case. This is not legal, tax, insurance or financial advice — confirm with a qualified professional or the relevant authority.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Indicative estimate only. Fees, entitlements, limits and formulas vary by jurisdiction, statute, policy wording and the facts of the case. This is not legal, tax, insurance or financial advice — confirm with a qualified professional or the relevant authority.

Frequently Asked Questions

What is a line?

One line equals the insurer's retention. A nine-line treaty therefore provides capacity of ten times the retention including the retention itself.

How does surplus differ from quota share?

Quota share cedes a fixed percentage of every risk. Surplus cedes only the amount above retention, so the insurer keeps 100% of small risks.