Percent off vs a fixed amount off
A percentage discount scales with the price — 20% off a $100 item saves $20, but 20% off a $10 item only saves $2. A fixed discount (like a $10 coupon) saves the same dollar amount regardless of price, so it is relatively more valuable on cheaper items and less valuable on expensive ones.
Working backward: finding the percent off
Sometimes you know the original price and the sale price but not the discount rate — a receipt, a sale tag, or an old order confirmation. Switch to Find % Off mode, enter both prices, and the calculator solves for the discount percent and dollar amount for you.
Why stacked discounts do not add up
When a second discount applies after the first, it applies to the already-discounted price — not the original. "20% off, plus an extra 10% off" is not 30% off: $100 → 20% off → $80 → 10% off → $72. That is an effective 28% discount, not 30%. Turn on "Add Stacked Discount" to model this exactly.
Discount first, then tax
In most places, sales tax is calculated on the discounted price, not the original price. When estimating your final checkout total, apply the discount first, then add tax to what is left — not the other way around.
Comparing two different discounts
To compare a percentage offer against a fixed-amount offer (or two stores’ discounts on the same item), work out the actual dollar savings for each — the calculator does this automatically so you can see which one genuinely saves more.