What is the percentage decrease formula?

Percentage decrease equals the starting value minus the final value, divided by the absolute value of the starting value, multiplied by 100.

Why is the numerator "starting minus final" instead of "final minus starting"?

Flipping the numerator keeps a normal decrease reading as a positive percent. Percentage Increase uses "final minus starting" for the same reason, in the opposite direction.

What does it mean if the result is negative?

A negative result means the value actually increased rather than decreased. Use a percentage increase calculator for the correctly labeled figure — the formula is the same, just read the other way.

If a value is cut in half, what is the percentage decrease?

Exactly 50%. Halving a value always corresponds to a 50% decrease, no matter how large or small the starting value is.

Does the formula still work when the starting value is negative?

Yes. The denominator uses the absolute value of the starting value, so the result stays meaningful even when the starting value itself is negative — for example, going from -10 to -15 is a 50% decrease.

How is percentage decrease different from a discount calculation?

A discount calculator usually goes the other way — it starts from a percent off and finds the reduced price. Percentage decrease starts from the two prices and finds the percent, which is useful for checking a discount was applied correctly.

Percentage Decrease Calculator

What is a percentage decrease?

Percentage decrease measures how much a value shrank from a starting point to a final point, expressed as a percentage of the starting value.

$\text{Percentage decrease} = \frac{\text{Starting} - \text{Final}}{|\text{Starting}|} \times 100$

Tip: The numerator is starting minus final — the reverse of Percentage Increase's final minus starting. Reversing it keeps an ordinary decrease coming out positive.

Worked example — LED light bulb

An old incandescent bulb uses 60W; a replacement LED bulb uses 8W. How much less power does the LED use, as a percent?

$60 - 8 = 52; \quad \frac{52}{60} = 0.8667; \quad 0.8667 \times 100 = 86.67\%$

The LED bulb uses 86.67% less power per hour.

Worked example — price drop

A jacket's price drops from $80 to $60.

$\frac{80 - 60}{80} \times 100 = \frac{20}{80} \times 100 = 25\%$

That's a 25% decrease in price.

Halving always means -50%

Going from 200 down to 100:

$\frac{200 - 100}{200} \times 100 = 50\%$

Cutting a value in half is always a 50% decrease — cutting it to a quarter is always a 75% decrease, and so on.

When the result is negative

The formula only measures the direction it's given — if the final value is actually larger than the starting value, the result comes out negative.

$\frac{100 - 200}{|100|} \times 100 = -100\%$

A negative percentage decrease means the value actually increased. The calculator flags this so the answer isn't misread as shrinkage — for a properly labeled figure, use the Percentage Increase calculator instead.

Negative starting values

The absolute value in the denominator keeps the formula meaningful even when the starting value is negative. Going from -10 to -15:

$\frac{-10 - (-15)}{|-10|} \times 100 = \frac{5}{10} \times 100 = 50\%$

That reads as a 50% decrease, matching the intuitive direction (the value moved further from zero, on the negative side).

Percentage decrease vs. percentage increase vs. percentage change

Tip: Percentage Decrease, Percentage Increase, and Percentage Change all use the same underlying idea — a change divided by |starting|, times 100. They differ only in which direction the numerator expects and how the sign is presented.

Reach for Percentage Change when you don't know in advance whether a value grew or shrank. Reach for Percentage Decrease (this calculator) or Percentage Increase when you're specifically checking for shrinkage or growth and want the label to match.

Percentage decrease vs. discount calculators

A discount calculator typically works forward — you know a percent off (like "20% off") and want the resulting price. Percentage decrease works backward — you know both prices and want the percent. Use this calculator to double-check that an advertised discount matches the actual price drop.

Common mistakes

Dividing by the final value instead of the starting value. The denominator is always the starting value, never the final one.
Forgetting the absolute value. Skipping the absolute value on the starting value can flip the sign when the starting value is negative.
Reading a negative result as shrinkage. If the percent comes out negative, the value went up, not down.

Where percentage decrease shows up

Retail and finance — markdowns, discounts, spending cuts.
Science and health — measurement reductions, weight loss tracking, energy savings.
Everyday comparisons — before/after reductions, efficiency improvements.