How to Calculate Percentages: The Complete Guide
Master every kind of percentage problem — finding a percentage of a number, percentage change, increases and decreases, working backwards, and the traps that catch people out — with clear examples.
Percentage Increase Decrease Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
New value
230.00
- Amount of change
- 30.00
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Percentage Increase Decrease Calculator
The Percentage Increase Decrease Calculator works out your new value, along with 1 related figure in an instant. Enter starting value, percentage and change and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the starting value.
- Enter the percentage.
- Choose the change.
- Read off your new value, together with amount of change — the calculator updates automatically, with no button to press.
Formula
The Percentage Increase Decrease Calculator uses the formula:
New value = Starting value + Change × Starting value × Percentage ÷ 100
Worked example
For example, with starting value of 200, percentage of 15% and change of Increase by, the new value is 230.00.
| Starting value | 200 |
|---|---|
| Percentage | 15% |
| Change | Increase by |
| New value | 230.00 |
|---|---|
| Amount of change | 30.00 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Percentage
- A number expressed as a fraction of 100, written with the % sign.
Frequently asked questions
Multiply the number by the percentage, divide by 100 and add it on. Increasing 200 by 15% gives 230.
Work out the percentage and subtract it. Decreasing 200 by 15% gives 170. Choose 'decrease by' to do this automatically.
Here you know the percentage and find the new value. Percentage change works the other way — it finds the percentage between two known values.
Yes. An increase over 100% more than doubles the value; a decrease cannot sensibly exceed 100%, which would take the value below zero.
The Percentage Increase Decrease Calculator uses the formula: New value = Starting value + Change × Starting value × Percentage ÷ 100. For example, with starting value of 200, percentage of 15% and change of Increase by, the new value is 230.00.
Enter the starting value. Enter the percentage. Choose the change. Read off your new value, together with amount of change — the calculator updates automatically, with no button to press.
Related guides
Percentage Increase Decrease Table: New value by Starting value
Reference table of new value for Percentage Increase Decrease across a range of starting value values — exact, engine-computed figures you can read off at a glance.
How to Calculate Percentage Increase Decrease: Formula, Steps & Examples
Learn how to calculate Percentage Increase Decrease — the formula explained step by step, with worked examples and a free calculator to check your answer.