Math walkthrough · single-discount arithmetic
What is 20% off of $80?
Straight answer first, then the formula, a mental-math route that works at the register, the same discount at nearby price points, and what changes when a second discount stacks on top.
20% off $80:
you pay $64
you save $16.00 — that's 20% of $80
The formula
The sale price is the original price times (1 − the discount as a decimal):
$80 × (1 − 0.20) = $80 × 0.8 = $64.00
The discount amount is 20% of the original price — $16.00 here — and what remains is the 0.8 multiple of the tag. Rounding happens once, at the end, to the cent.
Mental math route
Move the decimal one place left: 10% of $80 is $8.00. Take that 2 times off the tag:
$80 − $8.00 − $8.00 = $64.00
20% off at nearby price points
| Original | Discount | You pay |
|---|---|---|
| $40 | −$8.00 | $32 |
| $50 | −$10.00 | $40 |
| $60 | −$12.00 | $48 |
| $80 | −$16.00 | $64 |
| $100 | −$20.00 | $80 |
| $150 | −$30.00 | $120 |
| $200 | −$40.00 | $160 |
The full grid — every discount from 10% to 90% at these prices — is in the percent-off chart.
A second discount changes everything
If a store coupon takes another 20% off after the 20% discount, the two percentages multiply instead of add: 20% then 20% off $80 comes to $51.20 — an effective discount of 36%, not 40%. Check any multi-coupon price in the double discount calculator before you assume the total.
Frequently asked questions
What is 20% off of $80?
You pay $64.00. The discount removes $16.00 from the $80 tag.
How do I calculate 20% off in my head?
Move the decimal one place left: 10% of $80 is $8.00. Take that 2 times off the tag: The multiplier form — $80 × 0.8 — gets the same answer in one step.
Is 20% off the same as $16 off?
Only at exactly $80 — 20% of $80 is $16.00. At any other price the dollar figure moves with the tag, so the two offers are not interchangeable. The tradeoffs are worked through in dollar-off vs percent-off.
Is 20% off a good deal during Black Friday?
The percentage alone can't tell you — the same 20% sits on very different anchors. Before you buy, check the price history against the tag (the three-step anchor check in do prices rise before Black Friday), and if you're stacking store and manufacturer offers, the layer order in how to stack coupons on Black Friday decides what the final number really is.
Check it instantly
Put in the price and the percent — the engine returns the exact figure, and the 10%-steps show the mental-math route to it.
$64
you pay $64.00 — you save $16.00 (20% off $80)
Mental math route: $80 → −10% → $72 → −10% → $64
One discount layer only here — for stacked discounts use the main calculator, where percentages multiply instead of add.
Working the other direction — a receipt in hand and the original price missing? How to find the original price before a discount covers the reverse formula. And when the discount is written in dollars rather than percent, the successive discount formula shows how layered reductions combine.
Sources & verification
Sources last verified 2026-10-25. Retailer policies and sale calendars change without notice — treat the retailer's own help pages as the authoritative version before you buy.
Arithmetic is arithmetic; retailer rounding at the register (and how gift-card or tax interplay is handled) can differ by a cent from the pure figure.