Percentage Calculator

The percentage sums

• X% of Y = Y × X ÷ 100. For example 15% of 2,500 = 375.
• X is what % of Y = X ÷ Y × 100. For example 450 marks out of 550 = 81.82%.
• Percent change = (new − old) ÷ old × 100. A salary going from 40,000 to 46,000 is a 15% increase.
• Adding a percent = amount × (1 + X ÷ 100). Rs 1,000 plus 18% sales tax = Rs 1,180.
• Removing a percent that was added = total ÷ (1 + X ÷ 100). If Rs 1,180 includes 18% tax, the price before tax was Rs 1,000 — not 1,180 − 18%.

Questions

How do I calculate the percentage of marks?

Use “X is what percent of Y”: put your marks first and the total marks second. 450 out of 550 is 81.82%.

How do I work out a salary increase in percent?

Use “Percent increase or decrease”: put the old salary in From and the new salary in To. The answer shows the increase in percent and in rupees.

How do I add sales tax or GST to a price?

Use “Add or take off a percent”: enter the price and the tax rate (for example 18%). The first line is the price with tax.

How do I find the price before tax?

Enter the price that includes tax and the tax rate. The last line shows the amount before the tax was added.

Why isn’t a 10% rise followed by a 10% fall back to the start?

Because the second 10% is taken from a bigger number. 100 + 10% = 110, and 110 − 10% = 99.