Percentage Decrease Calculator

Calculate the percentage drop between two numbers, or find the original or final value after a percentage decrease.

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Percentage Decrease Calculator

The percentage decrease calculator shows how much a value drops from one amount to another, written as a percent. It also helps to know the percent decrease formula so you can do the math by hand.

Start with an original amount and a new amount. For a decrease, the new amount must be smaller than the original. First, subtract the new value from the original to find the drop. Next, divide that drop by the original amount. Then multiply by 100 to turn it into a percentage. You can also get a similar result with a percentage difference calculator or a percentage change calculator.

How to calculate percent decrease

To find the percentage decrease from an original value a to a new value b, follow these steps:

  1. Subtract the new value from the original: a − b.
  2. Divide by the absolute value of the original: (a − b) / |a|.
  3. Multiply by 100 to convert to percent.

That’s the full process. Once you’ve done it a couple times, it feels quick.

Percent decrease formula

Here’s the percent decrease formula in one line:

% decrease = 100 × (initial − final) / |initial|

Example of a percentage decrease

Say the original value is 750 and the new value is 590.

  • Find the difference: 750 − 590 = 160
  • Divide by the original: 160 / 750 = 0.213
  • Convert to percent: 0.213 × 100 = 21.3%

You can confirm the result with Omni’s percentage decrease calculator.

Real-life applications

Percent decrease comes up all the time when you want to describe a drop over time. A percent is often more helpful than the raw number because it shows the change in context.

For example, imagine a company earned $1,000,000 less profit than last year. That sounds serious, but it depends on where they started.

  • If last year’s profit was $2,000,000, the profit fell by 50%. That’s a major decline and a bad sign.
  • If last year’s profit was $100,000,000, the same $1,000,000 drop is only 1%. That still matters, but it’s not nearly as dramatic.

The percent drop gives a clearer picture than the dollar change alone.

Another common use is the population decline rate. This is the percent a population drops compared to the year before. If a town goes from 1,000 to 950 people, the decrease is 5% because:

100 × (1000 − 950) / 1000 = 5

Some countries see steady growth (like the USA or India). Others (like Japan) have seen population decline for years. Using a percent makes it easier to compare trends across places of different sizes.

A percentage shows how much one number is compared to another, based on 100 parts. For example, 3 out of 50 is the same as 6 out of 100, which is 6%. A simple method is:

(part ÷ whole) × 100

Percentages also help describe measurement accuracy. If you want to compare an observed value to a true value, use percent error (see the percent error calculator).

If you need the opposite of a decrease, you can use a percent increase calculator or calculate it by hand.

One helpful feature of a percentage decrease calculator is that it often shows both the raw difference and the percent difference. Sometimes you only need the number change, so having both options saves time.

Formula: Investopedia — investopedia.com

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People also ask

It measures how much a value dropped, compared to the starting (old) value, and expresses that drop as a percent.

A common formula is ((old - new) / |old|) × 100. In most everyday cases, the old value is positive, so |old| is just the old value.

You usually only need two numbers:

  • Old value: the starting amount (before the drop)
  • New value: the ending amount (after the drop)

The calculator subtracts, divides by the old value, then converts to a percent. It works with whole numbers and decimals, and it can also work with measurements like time (as long as both values use the same unit).

Use these steps:

  1. Find the drop: old - new
  2. Divide by the old value: (old - new) / |old|
  3. Convert to percent: multiply by 100

Then it isn't a decrease. Your result will come out negative, which signals an increase when you use the percent change form.

For decreases, you want the new value to be smaller than the old value. If it's larger, use a percentage increase or percent change calculation instead.

A common percent change formula is (new - old) / |old| × 100:

  • If the result is negative, the value went down (a decrease)
  • If the result is positive, the value went up (an increase)

Because the question is, "How big is the drop compared to where we started?" The starting point is the reference.

Using the new value as the base answers a different question, and it will give a different percent.

Absolute value keeps the denominator positive if the old value is negative.

Most real-world uses (prices, counts, weights) use positive starting values, so it doesn’t change anything. It just makes the formula safer for edge cases.

You can’t compute a percentage decrease from 0, because you’d be dividing by 0.

In plain terms, there’s no meaningful "percent decrease" from zero, since there isn’t a starting amount to compare against.

They sound similar, but they’re different tasks:

  • Percentage decrease: you already have old and new values, and you’re finding the percent drop.
  • Decrease by a known percent: you already know the percent, and you’re finding the new value.

A few errors show up a lot:

  • Swapping old and new: it flips the sign and changes the meaning.
  • Using the new value as the base: it answers a different question.
  • Forgetting to multiply by 100: you get a decimal instead of a percent (0.15 vs 15%).
  • Mixing units: for example, comparing minutes to hours without converting first.