What are the percentage increase and percentage decrease formulas?

The percentage increase formula multiplies the original value by one plus the rate divided by 100. The percentage decrease formula uses one minus that rate; both begin with the same original value.

Percentage increase and decrease formulas

Amount = Value × Percentage ÷ 100Increased = Value + AmountDecreased = Value − Amount

Two directions around one starting number

The default example calculates one percentage amount and uses it to show both the increased and decreased result around the same starting value.

Illustrative inputs; currency amounts below use USD. Rates and prices are assumptions, not live quotes.

Value
250
Percentage
15%

Step-by-step calculation

  1. Percentage amount = 250 × 15 ÷ 100 = 37.5.
  2. Increase: 250 + 37.5 = 287.5. Decrease: 250 − 37.5 = 212.5.

Intermediate figures are rounded for reading. Results use the full calculation precision.

After the increase287.5
After the decrease212.5
Amount of change37.5
Spread between the two75

Equal amount does not mean reversible percentage

The two adjusted values sit equally far from the original in absolute terms. When a higher result represents improvement, improvement percentage uses the same baseline comparison; returning from the decreased value requires a different rate because the base has changed.

The changed-base trap

A 20% decrease followed by a 20% increase does not return to the start. The second operation applies to the smaller new base.

  • The entered percentage is applied once to the original value.
  • Increase and decrease outputs use the same starting base.
  • No minimum, maximum or rounding rule is imposed beyond display formatting.

Calculations related to percentage increase and decrease

The following tools examine neighbouring parts of the same calculation without changing the inputs or assumptions used above.

References

Sources and conventions

Quick answers

Frequently asked questions

What is the percentage increase formula?

Increased value equals original value multiplied by one plus the percentage divided by 100.

What is the percentage decrease formula?

Decreased value equals original value multiplied by one minus the percentage divided by 100.

Is improvement percentage the same as percentage increase?

When both use the same original baseline and a higher result represents improvement, the calculation is the same percentage-change formula.

Why does reversing the same percentage not restore the original?

After the first change, the second percentage uses a different base, so equal percentage rates produce different absolute amounts.

Calculation method and limitations · Report an error

Educational content only. This guide is not financial advice.