Discount & Percent Calculator
Instantly compute discounted price, tax in/out, "what percent", and rate of change. Live results.
About this tool
Percentages are simple in principle, but the multiplication or division changes with each situation, making them easy to get wrong in your head. This tool separates the inputs by purpose, calculates in your browser, and never sends your input anywhere. Knowing the common traps makes checking much easier.
"Percent" and "percentage points" are different
When approval rises from 40% to 50%, the gap is "10 percentage points," but as a rate of increase it is "25% up" (10 Γ· 40). This distinction is often confused in the news and in reports, and mixing up which one you mean changes the impression a number gives dramatically.
Working back (pre-tax, original) is division, not subtraction
20% off 1,000 is 1,000 minus 200, or 800. But to get the pre-tax amount from a tax-included 1,100, it is not 1,100 β 10% but 1,100 Γ· 1.1 = 1,000. To undo "the amount after adding X%," divide back out what was multiplied in.
The same % up does not undo a % down
When 100 drops to 50, that is a 50% decrease, but getting 50 back to 100 requires a 100% increase. Because the base (the denominator) changes, applying the same rate in reverse does not return the original value. This is easy to misjudge when reading successive month-over-month figures.
Rounding can shift the result by a unit
Ratio calculations produce decimal fractions, so whether you round or truncate can change the final amount by a unit. For official amounts such as invoices, make a final check against the rounding rule you must apply.
How to use
- In "Discounted price", enter the price and discount (%) to get the final amount.
- "Tax included/excluded" converts both ways: enter price and tax rate (%), then pick a direction.
- "What percent" and "Rate of change" also update live as you type.
FAQ
Are the numbers I enter sent to a server?
No. All calculation is done in your browser, so the values you enter never leave your device.
How is "20% off" calculated?
The amount to pay is the original price minus the discount portion. For example, 20% off 1,000 is 1,000 minus 200, or 800. The tool shows both the amount to pay and the amount saved.
Can it compute tax-inclusive from tax-exclusive, or the reverse?
Yes. You can find the tax-inclusive amount from a tax-exclusive figure, or work back to the tax-exclusive amount from a tax-inclusive one. Enter the tax rate and switch as needed.
When would I use "what percent of Y is X"?
Use it to see how one value compares to a baseline β a progress rate toward a goal, a share of a total, or a test score percentage.
How do I find a rate of change (vs. last month or last year)?
Enter the before and after values and it computes the percentage increase or decrease. Handy for tracking sales, traffic, or weight over time.
How is rounding handled?
Ratio calculations produce decimal fractions, and the display is rounded to a set number of digits. Where a single unit matters, such as an invoice amount, make a final check using the rounding rule you must apply.
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<iframe src="https://tooldesk.dev/embed/en/tools/percent-calc" width="100%" height="600" style="border:1px solid #e5e7eb;border-radius:12px;max-width:640px" loading="lazy" title="Discount & Percent Calculator β ToolDesk" allow="clipboard-write"></iframe>
<p style="font-size:12px"><a href="https://tooldesk.dev/en/tools/percent-calc" target="_blank" rel="noopener">Discount & Percent Calculator</a> by <a href="https://tooldesk.dev" target="_blank" rel="noopener">ToolDesk</a></p>