---
title: "Percentage Calculator | Percent Of & Percentage Change | BQ Calculator"
canonical: "https://calculator.bqtools.com/percentage-calculator/"
description: "Calculate a percentage of a number, find what percent one value is of another, or calculate percentage increase and decrease with transparent formulas."
---

# Percentage Calculator

Solve the three percentage questions people use most: percent of a value, one value as a percent of another, and percentage change.

BQ Calculator · https://calculator.bqtools.com/percentage-calculator/

## Inputs

Share links contain only the values needed to recreate this calculation.

## Percentage result

## Percentage of a value

```text
result = value × percent / 100
```

Use this mode for discounts, tax amounts, commissions, progress and any question in the form “What is X% of Y?”

## One value as a percent of another

```text
percent = part / total × 100
```

This answers questions such as “30 is what percent of 120?” The total must be non-zero.

## Percentage change

```text
changePercent = (newValue - oldValue) / |oldValue| × 100
```

Using the absolute starting value keeps the sign tied to increase versus decrease. If the starting value is zero, the conventional percentage-change formula is undefined and the calculator says so explicitly.

## Precision

The engine retains JavaScript numeric precision during the calculation and rounds primarily for display. Inputs may include decimals and negative values where the selected formula has a meaningful result.

## Frequently asked questions

### How do I find a percentage of a number?

Multiply the number by the percentage written as a decimal. For example, 20% of 80 is 80 × 0.20 = 16.

### How do I find what percent one number is of another?

Divide the part by the total and multiply by 100. The total cannot be zero because division by zero is undefined.

### How is percentage change calculated?

Subtract the starting value from the ending value, divide by the absolute starting value, then multiply by 100. A positive result is an increase and a negative result is a decrease.

### What happens when the starting value is zero?

A conventional percentage change from zero is undefined because the formula divides by the starting value. The calculator shows an explanatory state instead of Infinity.

### Can this calculator be used for discounts?

Yes. Use the “percentage of a value” mode to find the discount amount, then subtract that amount from the original price.

### Related calculators

All calculation inputs stay local to this browser.

## Machine-readable resources

- Calculator registry: https://calculator.bqtools.com/calculators.json
- Site index: https://calculator.bqtools.com/llms.txt
- Full agent text: https://calculator.bqtools.com/llms-full.txt
- Agent discovery index: https://calculator.bqtools.com/agent-index.json