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Percent Increase vs Percent Decrease

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Direct answer

Both calculations use the original value as the baseline. Increase uses new − old; decrease magnitude uses old − new.

Formula and method

Increase = (new − old)/old × 100; decrease = (old − new)/old × 100

This page must show the formula exactly as the calculator or worked method uses it. Inputs remain unrounded during the calculation; rounding applies only to the displayed answer unless a domain-specific rule requires otherwise.

Step-by-step calculation

  1. Confirm the original is positive.
  2. Compare new with old.
  3. Choose the direction-specific numerator.
  4. Keep the original in the denominator.

Worked examples

80 to 100

Increase = 20 ÷ 80 = 25%.

100 to 80

Decrease = 20 ÷ 100 = 20%.

Round trip

A 25% rise from 80 reaches 100; a 20% fall from 100 returns to 80.

Interpretation and edge cases

  • Increase and decrease are not symmetric.
  • A result can exceed 100% for an increase, while ordinary decrease from a nonnegative value is capped at 100%.
  • Negative values need contextual interpretation.

Frequently asked questions

Can an increase exceed 100%?

Yes.

Can a decrease exceed 100%?

Not when a nonnegative quantity cannot go below zero.

Why are the reverse rates different?

They use different starting values.

Sources and transparency

The formulas and examples were evidence-checked on 2026-09-10. This is educational mathematical content. It does not replace a field-specific standard, accounting policy, laboratory method, contractual definition or professional judgment. CalculatorGeek should display a named human reviewer only after a real reviewer has completed and documented that review.

Use this resource

1 available tool
Open the Percent Change CalculatorRun the calculation with your own inputs, then return here to interpret it.

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