Percentage Calculator

Calculate percentages, percentage change, and ratios.

Mason ReidFounder and Lead Estimator at MeasureThen

Last updated 2026-08-21

What Is a Percentage Calculator?

The percentage calculator finds a percentage of a value, a percentage change, or a ratio, and rounds to two decimals. It is the everyday math tool behind discounts, taxes, progress billing, and bid comparisons. Homeowners use it to check a sale price or figure the share of a shared cost.

How It Works

Result = Value × Percentage ÷ 100.

Example

15% of 200 is 30.

How to Calculate

Enter the starting value, such as 200.
Enter the percentage you need, such as 15.
Read the result, which is the value times the percentage divided by 100. That gives 30.
Use the percentage change mode to compare an old and new value, such as a bid rising from $10,000 to $11,500.
Use the ratio view to show one number as a share of another, such as $1,000 within a $20,000 budget.

Common percentage formulas

Calculation	Formula	Example
Percent of a value	Value × Percentage ÷ 100	15% of 200 = 30
Percent change	(New minus Old) ÷ Old × 100	($11,500 minus $10,000) ÷ $10,000 = 15%
Value after discount	Price × (100 minus Discount) ÷ 100	$80 × 0.85 = $68
Value after tax	Price × (100 + Tax) ÷ 100	$100 × 1.06 = $106
Ratio as percent	Part ÷ Whole × 100	$1,000 ÷ $20,000 = 5%

Sources

Frequently Asked Questions

When is this useful on a job site?

For discounts, taxes, progress percentages, and comparing bid overruns.

Can I reverse it?

This tool finds the percentage of a value. For other conversions, combine it with the markup or waste calculators.

Does it handle decimals?

Yes — enter any value and percentage, and the result rounds to two decimals.

Mason ReidFounder and Lead Estimator at MeasureThen

Mason Reid founded MeasureThen after two decades of hands-on work in construction and estimating. Across residential and light commercial projects, he sized concrete pours, framed walls, hung drywall, and priced out roofing, fencing, and deck work — learning the exact math that every job depends on. At MeasureThen he writes the formulas, checks every calculator against real-world assumptions, and makes sure each one is simple enough for a homeowner to trust and a contractor to use. When he is not measuring twice, he is helping projects stay on budget.

Every MeasureThen calculator uses simple, transparent formulas and standard industry assumptions drawn from common construction practice. We show the math behind each result and include worked examples so you can follow along and double-check the numbers. Results are estimates: materials, labor, and pricing vary by region and market, so always confirm important figures with a licensed professional and your local building codes.