How to quickly subtract percentages?

The Shortcut to Quick Percentage Calculations

Calculating discounts or adding tax in your head doesn't need to involve a multi-step formula. Instead of finding the percentage first and then doing the extra math, you can get straight to the final answer with one simple multiplication.

When you need to subtract a percentage, focus on what remains rather than what is taken away. For example, if an item has a 20% discount, you are keeping 80% of the price. Simply multiply your original number by 0.8. You skip the middle step entirely and get your final discounted total instantly.

On the flip side, when you want to add a percentage—like calculating sales tax or a tip—you multiply the original number by 1 plus the percentage rate. Adding a 15% tip to a bill means you are looking for 115% of the cost, so you multiply by 1.15. Mastering these mental shortcuts saves time and keeps everyday math effortless.