Discount Calculator

Figuring out what a sale actually costs, or how big a discount really is, takes a bit of mental math that's easy to get backwards when you're standing in a checkout line or comparing deals online. This calculator handles both directions of that problem: enter an original price and a discount percentage to see the final price and exactly how much you're saving, or flip it around and enter a sale price and discount percentage to work out what the item cost before the markdown.

Forward mode answers "what will I actually pay?" It takes the original price and discount percentage and computes the amount saved as (original price × discount %) ÷ 100, then subtracts that from the original price to get the final price. This is the calculation behind reading a "30% off $80" tag and knowing on the spot that you'd pay $56 and save $24.

Reverse mode answers a less obvious but equally common question: "this item is on sale for $56 at 30% off: what did it cost originally?" You can't just divide the sale price by the discount percentage the way forward mode might suggest; the correct formula is original price = sale price ÷ (1 − discount % ÷ 100). This comes up when comparing a discounted price against a full-price competitor, or checking whether an advertised "original price" on a sale tag is actually accurate.

Both modes update their results live as you type, with no "Calculate" button to press, and a 100% discount in reverse mode (which would require dividing by zero) is flagged with a clear inline message instead of showing "Infinity" or a broken result. Every calculation runs as plain JavaScript directly in your browser, so nothing you type is ever sent to a server, logged, or stored anywhere.