Add or Subtract Percentage Calculator

1. Enter the starting number, percentage and add or subtract.
2. Read the highlighted result first, then the breakdown below it. Load the worked example to check the math by hand.

Adding or subtracting a percent means taking that percent of the starting number and adding or removing it. It is quicker to multiply by one combined factor.

• Amount = starting number × percent ÷ 100
• Add: result = starting number × (1 + percent ÷ 100)
• Subtract: result = starting number × (1 − percent ÷ 100)
• Reverse: original = number ÷ multiplier

The result is the starting number scaled by one combined multiplier. The reverse figure tells you what base would produce your number — useful for removing tax or markup already included.

Common mistakes and assumptions

• Subtracting a percent to undo an added percent (divide instead).
• Applying the percent to the wrong base.
• Adding percentages that apply in sequence.

Add 20% to 3,200.

1. 120% of 3,200 = 3,200 × 0.20 = 640.
2. 23,200 + 640 = 3,840 (or 3,200 × 1.20).
3. 3Reverse: 3,200 ÷ 1.20 = 2,666.67 is the number that becomes 3,200 after adding 20%.

How do I add 20% to a number?

Multiply it by 1.20. 3,200 × 1.20 = 3,840.

How do I subtract 15% from a number?

Multiply it by 0.85. 200 × 0.85 = 170.

Why doesn't subtracting 20% undo adding 20%?

The second step uses a bigger base. 100 + 20% = 120, but 120 − 20% = 96. To undo adding 20%, divide by 1.20 instead.

How do I remove tax already included in a price?

Divide by the multiplier rather than subtracting. A $108 price that includes 8% tax was $108 ÷ 1.08 = $100 before tax. The reverse result shows this figure.

What is “3200 x 20%”?

That is 20% of 3,200, which is 640. Adding it gives 3,840; subtracting it gives 2,560.