One book of gross losses, three cession mechanics, and one sign rule — learn exactly how a reinsurance program turns gross into net, with the same formulas a production pricing engine runs.
This is a hands-on course. You don't just read about cession — you run it. Every lesson has a live cell that executes on the page, and every lesson ends with a small calculation you do.
Who this is for
Anyone who needs to understand what actually happens to a loss when reinsurance is in place:
- actuaries starting out in P&C,
- underwriting assistants,
- developers building pricing or reserving systems,
- anyone who has stared at a term sheet saying "500 xs 250" and wanted to see the arithmetic.
You should be comfortable reading a little C#. No reinsurance background required — we start at why cede at all.
What you'll be able to do at the end
- Read gross / ceded / net as amount types in one cube — and know why ceded is stored negative
- Apply a quota share with a claims limit:
ceded = −min(cession% × gross, claimsLimit) - Apply an excess-of-loss layer:
ceded = −min(limit, max(0, loss − attachment)), per individual claim - Understand why attritional losses pass through an XL layer untouched
- Stack layers into a program and cap a year with aggregate deductibles and limits
- Trace every number back to one canonical loss book
How each lesson works
Every lesson has the same three bands:
| Band | What it is |
|---|---|
| 📖 Theory | The idea, kept short — with the exact formula from the engine. |
| ⚡ Experience it | A live code cell. It runs when the page loads — read the code, read the result, then change the numbers in your head and predict what happens. |
| ✍️ Your turn | A small exercise on the same loss book. A Peek at the solution link is always one click away. |
The worked example
Everything runs on one loss book — underwriting year 2025, two lines of business, six individual claims and one attritional amount — pinned in Lesson 1 and reused, unchanged, through the whole course.
The formulas are the real ones from MeshWeaver.Reinsurance, so the course teaches exactly what the engine computes.
The engine lives in that repo's Reinsurance module —
Reinsurance/Acceptance/Source,
CededCashflows.cs and CessionOperations.cs — whose in-node tests pin this course's numbers,
claim by claim.
Ready? Start with Lesson 1 — From gross to net.