Most flips look great on the back of an envelope: buy at 180k, sell at 280k, so 100k of profit. Then acquisition fees, a works overrun, eight months of carrying costs, loan interest and resale fees show up and the real figure shrinks.
I wanted a quick way to run those numbers without opening a spreadsheet each time, and without hiding my assumptions. So I wrote a Hermes skill, flip-margin-calculator, built around one standard-library Python script.
You give it a purchase price, a resale price and whatever else you know (works budget, contingency, holding months, monthly carrying costs, loan percentage and rate). It prints every assumption, a cost breakdown, net profit before tax, margin on resale price and on cost, return on equity, the break-even resale price, and the maximum purchase price for a target margin. A small sensitivity grid shows what happens if the resale price drops or the works run over.
python3 scripts/flip_margin.py --purchase-price 180000 \
--resale-price 280000 --works-budget 35000 \
--holding-months 8 --loan-ltc-pct 80 --target-margin 15
The defaults for fees and contingency are placeholders and are labelled as such. It does not give tax advice and does not look up prices. It is a sanity check, not a verdict.
A --selftest option checks the arithmetic and the solvers.
Skill (MIT): https://github.com/RobinBeraud/hermes-skills/tree/main/finance/flip-margin-calculator
All skills: https://github.com/RobinBeraud/hermes-skills
This post was written with AI assistance and reviewed through automated checks.
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