What to enter
- Original (list) price
- The price before any reduction, as printed on the product page. This is the number the discount is measured against.
- Discount %, or sale price
- Use "Find the sale price" when a store shows a percentage off. Use "Find the discount %" when you only know the two prices and want the real percentage.
- Extra coupon amount
- A flat amount (not a percentage) taken off the already-discounted price, such as an Amazon coupon. Leave it empty if there is none.
The formulas
- Saved amount = original price × discount % ÷ 100
- Sale price = original price − saved amount
- Discount % = (original price − sale price) ÷ original price × 100
- Price after coupon = sale price − coupon amount (never below zero)
A worked example
Made-up numbers: a jacket has a list price of ₹2,000 and is shown at 25% off, with a ₹100 coupon.
- Saved by the discount: 2,000 × 25 ÷ 100 = ₹500, so the sale price is ₹1,500.
- After the ₹100 coupon: 1,500 − 100 = ₹1,400.
- Total saving: 2,000 − 1,400 = ₹600, which is 30% of the original price.
Note that 25% off plus a ₹100 coupon is 30% in total, not 25% + 5%: the coupon is a flat amount, so its share depends on the price.
How to read the result
The discount is only as meaningful as the original price. If a listing's "original" price is one the product rarely or never sold at, a large percentage off tells you very little. Compare the sale price with what the product has actually cost recently, for example from the bot's recorded price history, rather than with the crossed-out number.
When you stack a percentage discount and a flat coupon, work out the final price and compare that figure between products or stores. Percentages on different list prices are not comparable with each other; final prices are.
Common mistakes
- Adding percentages together (for example 20% + 10% = 30%). A second percentage applies to the already-reduced price, so two successive percentage discounts give less than their sum.
- Measuring the discount against an inflated list price instead of the price the product actually sold for.
- Forgetting delivery fees, taxes or cancellation of an offer at checkout, which change the real final price.
- Comparing percentages across products with different list prices instead of comparing final prices.