SellerBox: Margin Calculator

■ SellerBox — the margin calculator built for online sellers

Selling on marketplaces like SmartStore, Coupang, Gmarket or 11st?
Enter your sale price and instantly see fees, contribution profit, margin rate and break-even ad spend — in real time, on one screen.
No spreadsheets. No formulas. Just answers.

■ Who it's for

• New sellers validating their first products
• Dropshippers and resellers who need quick margin checks
• Performance sellers deciding how much ad budget is safe
• Side hustlers running online shops

■ Key features

1. Real-time margin calculation
Enter sale price, purchase cost, fees, shipping, packaging and ad cost — profit and margin rate update instantly. A margin grade badge (loss / thin / healthy) shows your status at a glance.

2. Marketplace fee presets
Built-in fee rates for major Korean marketplaces (SmartStore, Coupang, Gmarket, 11st). Edit any rate or add your own custom marketplace.

3. Break-even ad spend (BEP)
Know exactly how much you can spend on ads before profit hits zero.

4. Target price & max purchase cost
Set a target margin and calculate backwards: the price you must charge, or the most you can pay for inventory.

5. Auto-saved history
Every calculation is saved on your device. Share result cards as images.

6. Settlement analysis (Excel · CSV · photo OCR)
Import marketplace settlement files or screenshots — fees and cost items are classified automatically.

7. VAT mode
Switch between simple mode and accurate mode (VAT-adjusted net profit).

■ How it calculates

Fee = sale price × fee rate + fixed fee
Profit = sale price − purchase cost − fee − shipping − packaging − ad cost
Margin rate = profit ÷ sale price × 100
Break-even ad spend = profit + current ad cost

■ Privacy first

No sign-up required. All calculations run on your device — your sales data never leaves it.
Privacy policy: https://ahgnodmik.github.io/sellerbox-privacy/

Find out in 3 seconds whether your product actually makes money.