Percentages look simple until a receipt, invoice, or promotion mixes multiple steps. Our percentage calculator, discount calculator, and stacked discount calculator exist because the mistakes are repeatable — and expensive.
Reverse percentages at checkout
“30% off” applies to the list price, not always to an already-reduced tag. When in doubt, compute the final price from original numbers you trust.
Stacked discounts are multiplicative
20% off then 10% off is not 30% off. Effective discount = 1 − (0.8 × 0.9) = 28%. Use the stacked tool when promotions combine.
Margin is not markup
Buy at $60, sell at $100: markup on cost is 66.7%, but profit margin on revenue is 40%. The profit margin calculator keeps the definitions straight for pricing SKUs.
Business KPIs
Percent change in revenue, conversion rate, and refund rate all use the same core algebra with different labels. Document which base period you compare so dashboards stay honest.