Methodology
This page explains how Profit For Sellers builds and maintains its calculators. Results are estimates for planning, not accounting, tax, or legal advice.
Calculation philosophy
Published calculators use deterministic formulas. They are not generated or AI answers. The same inputs produce the same outputs. Calculations run in your browser from the numbers you enter.
Percentages you type (such as a 2.9% payment fee or a 5% refund rate) are converted to the matching decimal form before they are used in the formulas. Currency symbols are for display; they do not change the math. Where refunds or other uncertain events matter, calculators use an expected-value mix of successful and unsuccessful orders based on the rate and recovery assumptions you set. Change those assumptions if they do not match how your business actually works.
Marketplace fee sourcing
Marketplace-specific fee assumptions are based on cited official platform documentation where applicable. Fee values are never invented. Not every possible fee worldwide is modeled. Presets are scoped to the markets and fee components documented on each calculator page.
The E-commerce Profit Calculator does not publish marketplace schedules; it applies a platform percentage only when you enter one. The Shopify Profit Calculator includes United States Basic, Grow, and Advanced online standard card rates and Shopify third-party transaction percentages from Shopify's official pricing documentation. The Etsy Fee Calculator includes a United States Etsy Payments schedule (transaction fee, processing, listing allocation, regulatory operating fee, and Offsite Ads cap) from Etsy's official Help articles. Additional Etsy countries are not auto-filled when that would require invented currency conversion. The TikTok Shop Fee Calculator includes United States 6% and 5% referral-fee presets from official TikTok Shop Seller University articles. Creator commission is user-entered. Non-US TikTok Shop markets, FBT rate cards, and special collectible or pre-owned referral tiers are not auto-filled.
The Break-Even ROAS Calculator and Product Pricing Calculator use user-entered payment and platform percentages only; they do not load marketplace or advertising-network fee tables.
Verification dates
Marketplace-specific calculators that ship sourced fee assumptions display or maintain a last-verified date for those assumptions where implemented. Check the calculator page for the date that applies to its presets and cited sources.
Update and maintenance policy
Profit For Sellers reviews marketplace-specific assumptions against official documentation and updates affected calculations and content when verified fee structures change. Platform schedules can change between reviews; sellers should still confirm current official rates for their account, market, and category.
Testing and quality control
Financial calculation logic is separated from UI where practical. Automated tests cover calculator logic so formula behavior can be checked independently of page layout. Each live calculator documents what it includes, what it leaves out, and which assumptions it uses.
Scope and limitations
Calculators are planning and educational tools. Actual platform charges can vary by account, plan, category, region, payment method, and promotions. Taxes, custom agreements, currency conversion, regional rules, and other costs may not always be modeled. A required selling price or break-even threshold is an economic result from your inputs and the disclosed model—not a claim that the market will pay it or that ads will hit that ROAS. Results are informational estimates. They are not a substitute for your books, tax filings, platform invoices, or professional advice. Verify platform-specific charges where it matters for your decisions.
Corrections
If you suspect a fee assumption is outdated or a calculation is wrong, use the Contact page. Reports that cite official documentation help keep sourced schedules accurate.
Browse live tools on the calculators hub or read the guides.