Percent Increase Calculator: Formula & Examples

The percent increase calculator on Calculator Soup works out how much a starting value has grown in percentage terms. You enter the original number and the new number, and it returns the percentage increase (or decrease) from the first to the second. This is the same calculation used for price rises, salary changes, population growth, and any before-and-after comparison.

Formula

The formula for percent increase is:

Percent Increase = ((New Value − Original Value) ÷ Original Value) × 100

• Original Value (a) – the starting amount, in any unit (dollars, people, grams, etc.)
• New Value (b) – the amount after the change, in the same unit
• Percent Increase (p) – the result, expressed as a percentage

If the new value is smaller than the original, the result is negative, which represents a percent decrease. Many calculators show the negative sign; some label it as “decrease” automatically.

Worked Example

Using the default values from the calculator above (original = 50, new = 75):

1. Subtract the original from the new: 75 − 50 = 25
2. Divide that difference by the original: 25 ÷ 50 = 0.5
3. Multiply by 100 to get a percentage: 0.5 × 100 = 50%

So a change from 50 to 75 is a 50% increase. The absolute increase is 25 units. The calculator rounds the percentage to two decimal places (e.g., 33.33% for a 1-to-1.333 change).

When to Use Percent Increase

Percent increase is useful whenever you want to express a change relative to the starting point, not just as a raw difference. For example:

• Price changes: a product goes from $20 to $25 – that’s a 25% increase, not just $5 more.
• Salary or rent adjustments: comparing a new offer to your current pay.
• Population or sales growth: year-over-year changes are usually reported as percentages.
• Grades or scores: a test score improving from 60 to 75 is a 25% increase.

The key is that the original value is the denominator. That makes percent increase different from absolute change – a $5 increase on a $10 item is 50%, but the same $5 on a $100 item is only 5%.

Common Mistakes and How to Avoid Them

Even with a calculator, errors happen. The most frequent ones:

• Swapping the original and new values. Always put the earlier (or smaller) value as the original. If you swap, you get a different percentage (e.g., 75 to 50 is a −33.33% change, not −50%).
• Using the difference as the numerator but forgetting to divide by the original. That gives you the absolute change, not the percent change.
• Confusing percentage points with percent change. If an interest rate goes from 4% to 5%, that’s a 1 percentage point increase, but a 25% increase relative to the original 4%.
• Rounding too early. If you round intermediate steps, the final result can be off. The calculator handles this internally, but if you do it by hand, keep extra decimals until the end.

Limits of the Formula

The percent increase formula assumes the original value is not zero. If the original value is 0, the formula divides by zero, which is undefined – you can’t express a change from zero as a percentage. In that case, you might report the absolute change instead.

Also, the formula gives a symmetric result for increases and decreases only in the sense that a 50% increase (50 to 75) is not reversed by a 50% decrease (75 to 37.5). To get back to the original, you need a 33.33% decrease. This asymmetry is inherent to percentage changes and is not a bug.

Finally, the result is a relative measure – it doesn’t tell you the magnitude of the change in absolute terms. A 10% increase on a $1 item is $0.10, while on a $1,000 item it’s $100. Always consider the context.

How to Use the Calculator

Using the Calculator Soup percent increase tool is straightforward:

1. Enter the original value in the first field.
2. Enter the new value in the second field.
3. Click the calculate button (or press Enter).

The result shows both the percentage increase and the absolute difference. If you need a percent decrease, simply enter a new value that is smaller than the original – the calculator will show a negative percentage.

You can also use the calculator in reverse: if you know the original value and the percentage increase, you can work out the new value by rearranging the formula: New = Original × (1 + Percent/100). Many people use the calculator for that as well, though it’s not the primary function.

Frequently Asked Questions

What is the difference between percent increase and percentage point increase?

Percent increase is a relative change – it compares the size of the change to the original value. Percentage point increase is an absolute change in a percentage itself. For example, if a tax rate goes from 10% to 15%, that’s a 5 percentage point increase, but a 50% increase relative to the original 10%.

Can I use this calculator for percent decrease?

Yes. If the new value is less than the original, the result will be a negative percentage, which indicates a decrease. For example, original = 80, new = 60 gives −25%, meaning a 25% decrease.

What if the original value is zero?

The formula becomes undefined because you can’t divide by zero. In such cases, percent increase is not a meaningful measure. You might instead report the absolute change or use a different metric.

How do I calculate percent increase without a calculator?

Use the formula: (New − Original) ÷ Original × 100. For example, from 50 to 75: (75−50) = 25, 25 ÷ 50 = 0.5, 0.5 × 100 = 50%. You can do this with a basic calculator or by hand.

Why is a 50% increase followed by a 50% decrease not back to the original?

Because percentages are relative to the current value. A 50% increase on 100 gives 150. A 50% decrease on 150 gives 75, not 100. To return to the original, you need a 33.33% decrease (50 ÷ 150 = 0.3333).

Does the calculator handle negative numbers?

Yes, but the interpretation changes. If both values are negative, the percent increase might be counterintuitive. For example, from −10 to −5, the formula gives ((−5) − (−10)) / (−10) × 100 = 5 / −10 × 100 = −50%, which is a decrease in absolute terms but an increase in value. It’s best to use the calculator for positive values unless you understand the context.

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in a | Original value | - | 50 | 0
in b | New value | - | 75 | 0
out p | Percent increase | % | ((b - a) / a) * 100 | 2
out diff | Absolute increase | - | b - a | 2