A live worked example you can take apart. It runs the canonical 2025 book of Alpina Versicherung AG through a real cession — Alpina keeps the first retention of every individual claim and cedes the rest — and shows gross, ceded and net side by side. The point of the lesson is on the totals line: because ceded is stored negative, net = gross + ceded holds on every row and when you sum the whole book. No subtraction anywhere.
This copy is yours to tinker with. Change retention and re-run:
- Set it to 1000 and only C5 cedes — the book barely moves.
- Set it to 200 and every big claim gives up its tail — watch ceded grow and net fall, while
net = gross + cededstays true on every line. - Edit a
Grossfigure, or drop a claim, and the totals still reconcile.
Run the 2025 loss book through a real cession: keep the first `retention` (start at 500) of every individual claim, cede the excess as a negative amount, and leave the attritional bulk untouched. Show gross, ceded and net per claim in a grid with a totals line proving net = gross + ceded, and make the retention a single variable I can change and re-run.
Everything above is self-contained: change a number, press Run, and read the new totals. When you are ready to be tested rather than shown, head to the Lesson 1 exercises.