Most stores do not fail because of traffic — they fail because the unit economics were never true. A product that looks profitable at a 40% gross margin can lose money after Shopify Payments fees, Amazon referral and FBA fees, shipping zones and a rising CAC. The calculators in this hub force every cost into the open, platform by platform, using current published fee schedules.
Start with margin: the Shopify and Amazon FBA tools show your true per-order profit. Then find your break-even ROAS before you spend on ads, and check that your LTV to CAC ratio justifies the spend. Operational tools — reorder points, churn impact, AOV simulation — then help you grow without stockouts or silent subscription losses. The sales tax and business loan tools cover the two obligations stores most often discover too late.
Each calculator shows its formula and works an example with realistic store numbers, so you can adapt the model to your own catalogue instead of trusting a single percentage someone quoted in a forum.
Which E-Commerce calculator should you use?
Checking a product's real profit on Shopify
Shopify Margin Calculator — includes COGS, payment fees and shipping in one margin.
Selling on Amazon
Amazon FBA Fee Calculator — deducts referral, fulfilment and storage fees by size tier.
Setting an ad budget
Target ROAS Break-Even — gives the minimum ROAS your margin can survive.
Judging acquisition spend
LTV to CAC Ratio — compares lifetime value with acquisition cost in one ratio.
Charging the right tax
Sales Tax & VAT — adds or extracts US sales tax and VAT correctly.
Why use DailyFinance for e-commerce calculations?
Every calculator on this page shows its formula, works through real-number examples, and explains what your result actually means — including the mistakes that make most online estimates wrong. Your inputs are calculated in your browser; if you create a free account you can save scenarios and come back to them, but no tool on this site requires sign-up. All tools are reviewed by Tahir Shehzad, ACMA, and updated for the current tax year and current platform fees where those apply.
- Free, no sign-up required
- Formula shown for every result
- Reviewed by a qualified finance professional