5 Percentage Tricks You Can Calculate in Your Head

Percentages show up everywhere — restaurant tips, sale discounts, exam scores. A few mental shortcuts can save you the trouble of reaching for a calculator for the easy ones.

1. Find 10% First, Then Adjust

10% of any number is just that number with the decimal point moved one place left. 10% of ₹450 is ₹45. Need 20%? Double it: ₹90. Need 5%? Halve the 10% value: ₹22.50.

2. X% of Y Equals Y% of X

This one surprises people: 8% of 50 is the same as 50% of 8, which is just 4. Whichever order is easier to compute in your head, use it — the answer is identical.

3. Calculating a Tip Fast

For a 15% tip, find 10% and add half of that again. On a ₹800 bill: 10% is ₹80, half of that is ₹40, so a 15% tip is ₹120.

4. Reverse Percentage for Discounts

If an item is 20% off and now costs ₹800, the original price was ₹800 / 0.8 = ₹1,000. A common mistake is adding 20% back to ₹800 (giving the wrong answer of ₹960) instead of dividing by (1 − discount).

5. Percentage Change

Percentage change = (new value − old value) / old value × 100. If a stock goes from ₹200 to ₹250, the change is (250−200)/200 × 100 = 25%.

For anything beyond quick mental math — or just to double-check your work — our percentage calculator below handles all of these cases instantly.