Percentage Increase Calculator
Find the percentage increase or decrease between two numbers. Enter the original and new values and the percent change is shown instantly — positive for an increase, negative for a decrease.
- 🔒 100% private — no uploads
- 🆓 Free, no watermark
- 📱 Works on any device
How to calculate
- 1
Enter the old and new values
Type the original number and the new number into the two boxes.
- 2
See the percent change
The increase or decrease is shown live as a percentage.
- 3
Switch modes if needed
Use the tabs to also find “% of a number” or “X is what % of Y”.
Why use Percentage Increase Calculator?
Increase & decrease
Positive results are increases, negative are decreases — both from the same inputs.
Instant
Updates as you type, entirely on your device.
100% private
Nothing is uploaded; the math runs in your browser.
Any device
No install or account needed.
The percentage change formula
Percentage change is (new − old) ÷ old × 100 — the difference measured against where you started. A price going from $80 to $100 is (100 − 80) ÷ 80 × 100 = +25%; dropping from $100 back to $80 is (80 − 100) ÷ 100 × 100 = −20%. Same $20, different percentage, because the base changed — which is why “percentage increase” and “percentage decrease” between the same two numbers are never mirror images.
Why +50% then −50% isn’t back to zero
Percentage changes don’t cancel out. Increase 100 by 50% and you’re at 150; decrease that by 50% and you land on 75, not 100. Each step is measured against a different base. The same trap appears in reverse: undoing a 20% drop takes a 25% rise. When you chain changes — sale prices, portfolio swings, growth rates — always compute each step from its own starting value, which is exactly what this calculator does.
Frequently asked questions
How do I calculate percentage increase?
(new − old) ÷ old × 100. For example, from 80 to 100 is a 25% increase.
What about a decrease?
The same formula gives a negative number for a decrease — from 100 to 80 is −20%.
Do my numbers get uploaded anywhere?
No. Every calculation runs entirely in your browser — your income, loan amount, balances and goals never leave your device. There’s no account and nothing is sent to a server.