Percent Off Calculator

Percent off is just a relationship

“Percent off” is a simple idea: it tells you how much cheaper something is compared to its original price. But the details matter. Is the discount applied once or stacked? Is tax added after discounts? Are there multiple coupons? Does the checkout round each line item? The difference between a quick estimate and the exact amount you pay usually comes down to those rules.

This Percent Off Calculator is designed for real shopping math. You can calculate the sale price from an original price and a discount percent, calculate the percent off from before-and-after prices, stack multiple discounts the way most carts do (multiplying the remaining price), and even reverse-calculate the original price if you only know the sale price and the percent off.

How percent off works

A percentage is a fraction out of 100. If something is 25% off, you’re saving 25 out of every 100 units of price. That means you pay the remaining 75%. In formulas:

This is why many people remember “multiply by what’s left.” A 25% discount leaves 75% to pay, so you multiply the original by 0.75.

Finding the percent off from prices

Sometimes the label isn’t clear, or you’re comparing deals. If you know the original price (P) and the sale price (S), the discount amount is P − S. The percent off is that discount divided by the original:

This is the fairest way to compare discounts across different price points because it expresses the reduction as a proportion of the original.

Stacked discounts: why they don’t add

A very common confusion is treating stacked discounts like they are additive. “20% off plus 10% off” feels like 30% off, but it usually isn’t. Most checkouts apply the first discount, then apply the second discount to the new lower price. That means you multiply the remaining fractions.

If discount 1 is d₁ and discount 2 is d₂, the final price is:

Example: 20% then 10% means you pay 0.8 × 0.9 = 0.72 of the original. That’s an effective discount of 28%, not 30%.

Effective percent off for multiple coupons

Even when multiple discounts are applied, you can convert the final result into a single effective percent off:

The Stack Discounts tab shows both the final price and the effective percent so you can compare “coupon stacks” with a straightforward “single discount” offer.

Where tax fits in the calculation

In many places, discounts are applied first and tax is calculated on the discounted subtotal. That’s what this tool’s “tax option” is meant to estimate: calculate the discounted amount, then add tax afterward.

However, real checkouts can vary. Some taxes apply differently to different product categories, some fees are taxed and some are not, and shipping may be treated separately. Treat the tax output as a planning estimate unless you know the exact tax rules for the checkout you’re using.

Reverse-calculating the original price

Sometimes you know the sale price and the percent off (maybe from a tag) and you want to know the “before” price. For a single discount, rearrange the sale price formula:

This can be useful when you see “28% off — now 72” and want to know if the claimed original price feels realistic. The Original Price tab calculates that quickly and shows the multiplier used.

Rounding differences and why your checkout can vary

If your numbers don’t match the checkout down to the last cent, that doesn’t always mean the math is wrong. Common reasons:

• Rounding policy: rounding per item vs rounding the final cart total.
• Tax timing: tax calculated before discounts, after discounts, or per line item.
• Fees: shipping, service fees, or payment fees added after discounts.
• Coupon rules: some coupons exclude certain categories or cap the discount amount.

The calculator helps you understand the “clean math” of the discount. If your checkout differs, check the order: discount(s), then tax, then fees — and whether rounding happens at each step.

Smart ways to compare deals

Two deals can look similar on the label but differ in total value. To compare fairly:

• Compare effective percent off when discounts stack.
• Compare final price after tax if tax rates differ by location or store type.
• Include any required spend thresholds or shipping minimums.
• Watch for “up to” discounts and exclusions.

Common shopping scenarios

Single discount on one item

Use the Sale Price tab. Enter the original price and percent off to get the discounted price and savings. Add tax if you want an estimated total.

Comparing a coupon stack to a single discount

Use the Stack Discounts tab. It will compute the final price and the effective percent off, then show the equivalent single-percent discount.

Checking a claimed “was” price

Use the Original Price tab. Enter the sale price and percent off, then compare the estimated original to what the store claims.

Finding the percent off from two prices

Use the Find Percent Off tab. Enter the original and sale price, and the tool will compute both the discount amount and the percent off.

Quick formulas to remember

• Sale price: sale = original × (1 − p/100)
• Savings: savings = original − sale
• Percent off: p = ((original − sale) ÷ original) × 100
• Stacked price: final = original × Π(1 − pᵢ/100)
• Effective percent off: 100 × (1 − final/original)