| Scenario | Percent | Base | Result | Status |
|---|
A percentage calculator helps you answer several common questions quickly. You may want to know what 15% of 240 is, what percent one number is of another, how much something increased, or what the original value was before a discount or markup. This page combines those jobs into one tool so you do not need separate formulas every time.
The most important thing is choosing the right mode. If you are finding part of a number, use percent of. If you are comparing two values, use what percent. If something moved from one number to another, use change. If you only know the final value after an increase or decrease, use reverse percent.
| Mode | What it answers | Typical use | Common mistake |
|---|---|---|---|
| Percent of | How much is X% of Y? | Tax, tip, commission, discounts | Using the percent as a whole number |
| What percent | X is what % of Y? | Share of total, contribution, ratios | Swapping part and whole |
| Change | How much did it rise or fall by %? | Prices, traffic, revenue, scores | Using new value as the base |
| Increase/decrease | What is a value after adding or removing %? | Markup, discount, budgeting | Adding the percent directly |
| Reverse % | What was the value before a % change? | Pre-discount or pre-tax values | Subtracting the percentage instead of reversing it |
Most percentage errors happen because people mix up the base number. A 20% rise from 100 to 120 is not the same as a 20% fall from 120 back to 100. The base changes the answer. That is why price discounts, margin comparisons, and reverse-percentage questions often feel confusing.
This calculator reduces that friction by using plain-language modes. Instead of forcing you to remember formulas, it lets you choose the exact question first, then gives you the number and a readable explanation of what happened.