How this instrument works
A percentage discount does one job: it splits a starting price into two dollar amounts, what remains and what is removed, using a single multiplication for each. It is the simplest member of a small family of retail formulas — stack two of these and you get a compound reduction, add a cost figure underneath and you get margin erosion — but on its own it takes no opinion on cost, tax, or a second offer layered on top. That narrowness is the point: one price, one percentage, two numbers back.
The two questions it answers come up constantly outside a single storefront transaction. A shopper comparing a 20% code against a 15% code on differently priced carts cannot rank the percentages alone, because the dollar savings depend on the base each is applied to. A person reselling furniture or electronics who prices items at a flat percentage below an estimated retail value is running the same formula in reverse, treating the estimate as the starting figure rather than a store's tag.
It is easy to point this instrument at the wrong base. A discount is always taken from the selling price, never from what something cost the seller to acquire — that second, cost-based calculation is a markup, and it moves the price in the opposite direction. Twenty percent off a $100 price and a 20% markup on an $80 cost use the identical rate but land on different figures, $80.00 against $96.00, because one subtracts from the top and the other adds from the bottom.
- Enter the pre-reduction figure into Original price, $ — the amount before any percentage is applied.
- Set Discount, % to the rate being taken off, such as 15 for a fifteen-percent cut or 62.5 for a fractional clearance rate.
- Read Final price, $ for the exact amount left once the percentage is removed.
- Read Amount saved, $ alongside it — the two figures always sum back to Original price, $.
- Re-run the sheet on a second offer or a second item to compare Amount saved, $ across them directly, rather than comparing the bare percentages.
Worked example — a $100 gift card at 20% off
Retailers periodically sell gift cards below face value as a promotional draw — pay less today for a card that spends at full value later. Set price to 100 and discountPercent to 20: finalPrice comes out to 100 × 0.80 = $80.00, the amount charged at checkout, and savings comes out to 100 × 0.20 = $20.00, the discount built into the card before it is ever used.
That $20.00 figure is only meaningful next to a comparable offer. A $150 speaker at 15% off saves $22.50 — a smaller percentage producing a larger dollar saving, purely because it is taken from a bigger starting price. Reading Amount saved, $ from two runs of this sheet side by side settles the comparison; ranking 20% against 15% on their own does not.
Questions
Does a bigger percentage always save more money?
No. Savings in dollars depend on the price the percentage is applied to, not the percentage alone. Twenty percent off a $100 gift card saves $20.00, while fifteen percent off a $150 speaker saves $22.50 — the smaller rate wins because its base is larger. Compare Amount saved, $ across two runs of this sheet rather than ranking the percentages by themselves.
How is a percentage discount different from a markup?
A discount is measured against the selling price and subtracted from it; a markup is measured against the seller's cost and added to it. Twenty percent off a $100 price gives $80.00 here, but a seller who paid $80.00 for that item and applied a 20% markup would charge $96.00 — the same rate, opposite direction, and a different base entirely. The two figures are not interchangeable.
What happens if I enter a discount over 100%?
The arithmetic keeps running past the point that makes retail sense: at 150%, Final price, $ turns negative and Amount saved, $ exceeds Original price, $. Nothing in the formula stops this, because a multiplication has no natural ceiling — a real markdown does, since no store pays a customer to remove an item. Treat a negative Final price, $ as a sign the percentage was mistyped.
Does this include sales tax?
No. Final price, $ is the pre-tax amount left once the percentage is removed, not what a register ultimately charges. Most U.S. states apply sales tax to the already-discounted figure rather than the original price, so a tax calculation belongs as a separate step applied after this one, not folded into either output here.
Why do Final price, $ and Amount saved, $ always add up to Original price, $?
Because they are complementary shares of one figure — the portion kept and the portion removed — and a share plus its complement always equals the whole. If you re-enter the numbers and the two outputs stop summing to Original price, $, a digit was mistyped somewhere in either the price or the percentage.
Can this compare a percentage coupon with a flat-dollar coupon?
Yes. Enter the cart price and the coupon's percentage, then compare Amount saved, $ against the flat figure printed on the other coupon. A 20%-off code on a $40 cart saves $8.00 — less than a flat $10-off code on the same cart — but above a $50 cart the percentage code overtakes it. Running both against the same base price shows which is larger for that specific total.
References
- FTC — Guides Against Deceptive Pricing, 16 CFR Part 233
- U.S. Small Business Administration — pricing guidance for small firms
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.