Calculating percentage increase is one of the most useful skills in everyday math — whether you're comparing salaries, tracking investment returns, or checking how much that coffee has gone up in price. The good news: it comes down to a single, memorable formula.
This guide walks you through the formula, demonstrates it with worked examples, and explains each step in plain English. You can also use our free percentage increase calculator to check your work instantly.
The Percentage Increase Formula
Here is the formula you need:
A positive result means the value increased. A negative result means it decreased. The formula works identically in both cases — the sign of the output tells you the direction.
Step-by-Step Walkthrough
Let's apply the formula to a concrete example: a product price rises from $80 to $100.
Step 1 — Find the difference. Subtract the original value from the new value:
$100 − $80 = $20
Step 2 — Divide by the original value. Use the absolute value of the original (which is just $80 in this case):
$20 ÷ $80 = 0.25
Step 3 — Multiply by 100. Convert the decimal to a percentage:
0.25 × 100 = 25%
The price increased by 25%.
Quick tip: You can skip step 3 by thinking in terms of fractions. 20/80 = 1/4 = 25%. For round numbers, this mental shortcut is faster than reaching for a calculator.
Example 2: A Value That Decreases
The same formula handles decreases automatically. A stock falls from $320 to $256.
Step 1: $256 − $320 = −$64
Step 2: −$64 ÷ $320 = −0.20
Step 3: −0.20 × 100 = −20%
The stock dropped by 20%. Notice that the formula gave us a negative number automatically — no special rule needed for decreases.
Handling Negative Original Values
What if your starting value is negative? Say a business had a loss of −$500 last quarter but a loss of only −$300 this quarter — an improvement.
Step 1: −$300 − (−$500) = +$200
Step 2: +$200 ÷ |−$500| = +$200 ÷ $500 = +0.40
Step 3: 0.40 × 100 = +40%
The loss improved by 40% — the absolute value in the denominator is critical here. Without it, you'd get the wrong sign and misread the direction of change.
Can Percentage Increase Exceed 100%?
Yes — and it's more common than you'd think. If a value doubles, that's a 100% increase. If it triples, that's 200%. There is no ceiling. A startup that grows revenue from $100K to $1M has achieved a 900% increase.
Common Mistakes to Watch For
The most frequent error is swapping the original and new values. Always put the original in the denominator. If you reverse them, you'll calculate the percentage the new value is of the old value — a completely different question.
The second most common mistake is forgetting the absolute value when the original is negative. This leads to a flipped sign and an incorrect interpretation of whether things improved or worsened. For a deeper look, read our guide on 5 common percentage increase mistakes.
When to Use a Calculator vs. Mental Math
For round numbers and simple fractions (halves, quarters, tenths), mental math is fast. For anything else — especially decimals, large numbers, or financial data where precision matters — use our percentage increase calculator. It handles the arithmetic instantly and shows every step so you can verify the logic.
Want to see where this skill shows up in the real world? Check out our article on 10 real-world uses of percentage increase.