Discount Calculator

How to use this calculator

Three tabs, three different discount scenarios. Pick the one that matches your situation.

Tab 1: Single Discount handles the most common case. Enter the original price, a discount percentage or a flat dollar discount amount, and an optional sales tax rate. The calculator shows your final price, the dollar amount you save, your savings as a percentage, and any tax applied.

Tab 2: Multiple Discounts handles coupon stacking and layered promotions. Enter up to three discount percentages applied to the same item. Choose whether they stack (each applied to the reduced price) or are separate (each applied to the original price separately then combined). This is the difference between saving more than you expect and saving less.

Tab 3: Reverse (Find Original) is for when you know the sale price and the discount percentage, but want to recover the original price. Useful for resale pricing, audit work, or figuring out what an item “really” costs before a sale.

How to enter discounts: You can enter either a percentage (like 25 for 25% off) or a specific dollar amount off. Use the toggle to switch between the two modes. Dollar-off discounts are common on store coupons and loyalty rewards.

Sales tax: Enter it as a percentage. Tax is always applied to the post-discount price, not the original price. A 20% discount followed by 8% sales tax means you pay tax on the discounted price, which is how every US state handles it.

What discount math actually does

A discount percentage is a reduction applied to a base price. The math is simple, but the nuances compound quickly when you stack promotions or add tax.

Percentage discounts remove a fraction of the original price. A 25% discount on a $100 item removes $25, leaving $75. The formula is straightforward:

Dollar-off discounts remove a fixed amount regardless of price. A $20 off coupon on a $100 item gives the same $20 savings whether the item is $80 or $200. However, the percentage saved is different in each case.

Stacked discounts are where most people make mistakes. When two discounts are applied sequentially, the second discount applies to the price after the first discount, not to the original price.

This is always less savings than adding the percentages together. 30% off followed by 20% off gives an effective discount of 44%, not 50%.

Reverse calculation works backward from the sale price to the original:

The stacking trap

The most common misconception in discount math is treating stacked discounts as additive. They are not.

Here is why it matters:

The larger the discounts, the bigger the gap between what shoppers think they are saving and what they actually save. Retailers know this. “50% off, plus an extra 50% off” sounds like a free item but is actually 75% off. Still good, but not free.

Perceived savings always exceed actual savings when discounts stack. The gap grows exponentially as the discount sizes increase.

The reverse is also true: when a retailer applies discounts separately to the original price and then combines them, the savings are additive. This is rarer and usually seen in specific promotional structures like military discounts applied independently of sale prices.

Real-world examples

How sales tax interacts with discounts

In most jurisdictions, sales tax is applied to the final sale price after all discounts. This is good for you as the buyer: you pay tax on less money.

The calculation order matters:

1. Start with original price
2. Apply all discounts
3. Apply sales tax to the discounted price

Some states have different rules. In a handful of cases, if a coupon is issued by the manufacturer rather than the retailer, the retailer may collect tax on the pre-coupon price and then submit the coupon amount as a reimbursement. This mostly affects grocery coupons and is handled at the register automatically.

For practical purposes, when you are shopping, tax applies after discounts. The only exception you might encounter is gift cards: some states tax the face value of a gift card at purchase, which can feel like double taxation when you use it to buy a discounted item.

Markup versus markdown

Discount calculations run in two directions, and the terminology matters if you are on the selling side.

Markdown starts at the retail price and removes a percentage. A 30% markdown on a $100 item gives a $70 sale price. This is the standard consumer discount.

Markup starts at cost and adds a percentage to reach a retail price. A 30% markup on a $70 cost gives a $91 retail price. Note that a 30% markup is not the same as a 30% margin.

This creates a common confusion in business contexts:

A 30% margin means cost is 70% of the sale price. A 30% markup means cost is 77% of the sale price (because cost / (1 + 0.30) = cost / 1.30).

If a retailer buys an item for $70 and marks it up 30%, they price it at $91. If they then offer 30% off, the sale price is $63.70, which is below cost. This is why retailers almost never discount by the same percentage they marked up.

Practical shopping tips

Use the reverse calculator before trusting “original prices.” Many online retailers inflate original prices to make discounts look larger. If you see “$199.99, now $79.99 (60% off),” check: $79.99 / (1 - 0.60) should equal $199.98, which checks out. If the math does not work, the original price is inflated.

Stack discounts in the right order when you have a choice. If one discount is a fixed dollar amount and another is a percentage, apply the percentage first. A 20% discount plus a $10 coupon on a $100 item: applying 20% first gives $80, then $70 final. Applying $10 first gives $90, then $72 final. Same discounts, different order, different savings.

Cashback portals compound your savings. If you shop through a cashback site that pays 5% and the store offers 30% off, your effective discount is the stacked result: 35% of the original, roughly. Some people run three layers: sale price, coupon code, cashback portal.

Sales tax on discounted items can shift buying decisions. A $500 item with 10% tax is $550. A $500 item with 30% off plus 10% tax is $385. The tax on the full-price item is $50; on the discounted item it is $35. You save $15 in tax alone by buying during the sale.

The bottom line

Discount math is simple in theory and surprisingly tricky in practice, mostly because of stacking and the additive vs. multiplicative confusion.

The key things to remember: stacked discounts multiply, not add. Tax always applies to the discounted price. The reverse formula recovers original prices and helps you verify claims.

Use the Single Discount tab for everyday calculations. Use Multiple Discounts when you are stacking promotions. Use Reverse to fact-check a sale or work backwards from a final price. The calculator handles all three cases instantly, so you never have to do the mental arithmetic in the store.