Margin Master — E-commerce Profit Calculator

Know exactly what each SKU earns — after every fee, shipping cost, ad dollar, and return.

What you get

• True per-unit profit — price, product cost, inbound freight, marketplace fees, fulfillment/shipping, ad spend, and returns folded into one number
• 5 marketplace presets — Amazon, eBay, Shopify, TikTok Shop, Etsy
• Contribution margin & ROI per SKU, ranked best to worst
• Break-even units — how many you must sell to cover fixed costs
• Break-even ACOS — the ad-spend ceiling each SKU can afford
• Monthly P&L — total contribution, fixed costs, net profit
• Thin-margin warnings — flags any SKU under 10% margin before a fee change or returns spike wipes it out
• CSV export — one row per SKU for your own spreadsheets

Honest by design

• Fee presets are estimates, clearly labeled. Every report prints the exact values used, and you can override any of them with your real numbers from your seller account.
• Losses are reported plainly. If a SKU loses money, the report says so and shows which cost line drives it.
• No affiliate links, no upsells, no data leaves your machine. Pure Python, stdlib only — no dependencies, no network calls.

Who it's for

Amazon FBA sellers, eBay resellers, Shopify store owners, TikTok Shop and Etsy sellers — anyone who has ever wondered "am I actually making money on this?"

How it works

1. Tell the skill your SKUs: marketplace, price, costs, shipping, ad spend
2. Confirm the fee assumptions (or enter your real ones)
3. Get the report — ranking, P&L, break-even, warnings, CSV