Percentage Decrease Calculator

Percentage Decrease Formula

One compact formula powers discounts, KPIs, grades, and population summaries, as long as the baseline is the starting value.

Percentage Decrease Calculator

Quick answer

Percent decrease compares the drop to the original value: subtract new from original, divide by original, multiply by 100.

((original − new) / original) × 100

Introduction

If you already use spreadsheets, this is the same ratio you would lock into a single cell before copying down a column.

Main content

What the formula is doing

The numerator is the amount of decrease in the same units as the baseline. Dividing by the baseline rescales that drop into “per one hundred units of baseline.”

Multiplying by 100 converts the decimal into a familiar percent display.

Formula in symbols

((starting value − new value) / starting value) × 100

Some textbooks label “original” and “new.” Keep the mapping consistent on every slide: readers should never guess which number sits in the denominator.

When the new value exceeds the starting value, the numerator flips sign. The magnitude still tells you how large the move is relative to the baseline.

Step-by-step breakdown

  1. Write O for original and N for new.
  2. Compute O − N.
  3. Divide (O − N) by O.
  4. Multiply by 100.
  5. Optional: round for display, keep extra digits for downstream calculations.

Worked example

Hours billed drop from 1,200 to 960. ((1,200 − 960) / 1,200) × 100 = 20%.

If someone mis-places 960 in the denominator, the percentage will not match the story. Double-check cell references in Excel.

FAQ

Can the result exceed 100%?
Yes, when the new value is negative while the original is positive, or when the drop is larger than the original in magnitude. Explain those cases carefully.
Should I use absolute value on the denominator?
For the standard decrease definition here, the baseline is the stated starting value. If your domain uses signed baselines, align with your finance or data policy first.

Conclusion

Summary

The formula is short; the discipline is naming the baseline and using it consistently.

Plug pairs of values into the Percentage Decrease Calculator whenever you want a second opinion on the arithmetic.

Open the calculator

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