How to use the Original Value Calculator?

Enter the percentage and the resulting number (the part). The calculator finds the original whole number.

How does the Reverse Percentage Calculator work?

It finds the base value using the formula: Original Value = Number / (Percentage / 100). For example, if 20 is 10% of a number, the original number is 20 / 0.10 = 200.

Original Value Calculator

What is the original value if X% of it equals Z?

Round

Entering 0 here causes a division by zero error.

Contextual hints will appear here as you calculate

Expand on save

Maximum of 20 saved calculations reached. Remove existing ones to save new ones.

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Max

Help

The Original Value calculator (also known as reverse percentage calculator) helps you find the original value when you know a percentage and its result. This is useful for working backward from a known percentage to find the original amount.

Practical Uses

Pre-Discount Price:
25% [X] of what original price [Y] is a £50 [Z] discount on a smartwatch?
£200

Pre-VAT Amount:
20% [X] of what pre-VAT amount [Y] is £40 [Z] VAT?
£200
Original Value:
15% [X] of what dinner bill [Y] is a £30 [Z] tip?
£200
Pre-Rise Salary:
10% [X] of what original base salary [Y] is a £4,000 [Z] pay rise?
£40,000
Investment Principal:
12% [X] of what original ISA balance [Y] is a £2,400 [Z] return?
£20,000
Total Budget:
30% [X] of what total Christmas budget [Y] is £600 [Z]?
£2,000

How to Use

Enter the percentage in the first box.
Enter the part value in the third box.
The original value appears instantly in the middle box.
Check "Round" if you want to keep the result to two decimal places.
Save it to your list with Enter or the "Save calculation" button.

How It Works

The Original Value calculator uses this formula:

\text{Original Value} = \frac{\text{Result} \times 100\%}{\text{Percentage}}

Example: If 15% equals 30, the original value is:

\frac{16 \times 100\%}{20} = 80

So the original value is 200.

Important Note

When the percentage is 0%, the calculation is undefined because you cannot divide by zero.

What Is a Reverse Percentage Calculation?

Definition

A reverse percentage calculation finds the total when you only know a piece and what percent that piece represents. It is like holding one slice of pie and knowing it is 10% of the pie; reverse percentage tells you the pie's full size. This matters anywhere you see a part and a rate but not the whole: market share reports, fundraising progress bars, net salary after taxes, or discounts expressed as pounds saved. Working backward keeps you from guessing and lets you rebuild the base number with confidence. It also exposes marketing tricks—for example, 'save £40 at 20% off' instantly reveals the original £200 price. Because the maths uses division, small errors in the percent guess can shift the result, so using an exact calculator avoids off-by-a-bit outcomes. It is especially handy when auditing invoices or pay stubs that list only withholdings or partial amounts—you can recompute the gross to check accuracy.

Common Applications

Market Sizing: Estimating the total revenue of an entire industry when you know one company's revenue and their market share percentage.
Salary Planning: Determining how much gross income you need to earn in order to take home a specific target amount after taxes.
Fundraising Goals: Calculating the total donation target if the current funds raised represent only a small percentage of what is needed.
Reverse Sales Analysis: Figuring out the original listing price of a clearance item if you know how many pounds you saved and what the discount rate was.
Commission maths: Recovering total sales volume from the commission pounds earned at a known rate.
Tax gross-up: Finding the pre-tax amount needed to land at a specific net pay.

Mathematical Context

Whole = Part ÷ (Percent/100)

Use the inverse of the forward formula: if £50 is 10% of a budget, divide £50 by 0.10 to get a £500 total. If savings of £40 came from a 20% discount, the original price is £40 ÷ 0.20 = £200. The division step is critical because subtracting or adding the percent to the part will not restore the base. For accuracy, enter percents as decimals (15% → 0.15) and avoid rounding until the final step. When percents stack (like commission on top of tax), work with the exact percent that applies to the piece you know, or decompose the stack to avoid drift.

Need more percentage tools?

Basic Percentage Calculator
For discounts or taxes.
Part-to-Whole Percentage
Find what % one number is of another.
Percentage Change Calculator
Work out increases or decreases.
Increased Value Calculator
Calculate value after percentage increase.
Decreased Value Calculator
Calculate value after percentage decrease.
Original Before Increase Calculator
Find original amount before percentage increase.
Original Before Decrease Calculator
Find original amount before percentage decrease.
Specialized Calculators (63+)
Practical everyday calculations for real-life scenarios.

Requirements and Important Information

No installation required – works directly in your browser.
Compatible with all modern browsers (Chrome, Firefox, Safari, Edge).
Calculations are performed locally – no data is sent to any server.
Your saved calculations are stored only on your device.
Each calculator stores up to 20 most recent calculations, automatically removing the oldest entries when this limit is reached.
Works offline after the initial page load.
Supports both desktop and mobile devices.
No account or login required.

Helpful Calculator Features

Instant results that appear as you type—no delays.
Round toggle to keep results neat (2 decimal places).
Copy results to clipboard with a single click.
Saved calculations that persist between sessions.
Clear visual formulas to understand the maths.
Mobile-friendly interface that works on all devices.
Dark mode support for comfortable viewing.
Keyboard shortcuts for faster calculations.