TallyBench / Percentage Calculator
Six tools that cover the percentage questions people actually ask — percent of a number, what percent one number is of another, reverse percentages, change over time, quick increase/decrease, and percentage difference. All update live as you type.
The classic — discounts, tips, commissions.
Test scores, market share, progress toward a goal.
Reverse percentages — work back to the original amount.
From an old value to a new value — prices, salaries, traffic.
Add VAT, apply a raise, take off a discount.
Compare two values with no "before" and "after" — measured against their average.
Everything the six tools above are doing, explained.
A percentage is just a fraction with 100 as the denominator — the word literally means "per hundred." Saying 25% is the same as saying 25 out of every 100, the fraction 1/4, or the decimal 0.25. That single idea powers every tool on this page; what changes between them is which piece of the puzzle you already know and which one you're solving for.
Multiply Y by X and divide by 100: X% of Y = Y × X ÷ 100. This is the workhorse of everyday life. A 20% tip on a $64 dinner in the US is 64 × 20 ÷ 100 = $12.80. A 15% discount on a €90 jacket is €13.50 off. GST at 18% on a ₹2,500 service is ₹450. Any time you know a rate and a base amount, this is the formula.
Divide the part by the whole and multiply by 100: (A ÷ B) × 100. Scoring 42 out of 60 on an exam is (42 ÷ 60) × 100 = 70%. If your team closed 30 deals out of 120 leads, that's a 25% conversion rate. The order matters — the number after "of" is always the denominator.
Divide the known result by the percent expressed as a decimal: original = Z ÷ (X ÷ 100). If a 15% deposit on a home came to $45,000, the home price was 45,000 ÷ 0.15 = $300,000. This mode also answers the very common "price before tax" question — if a receipt shows €121 including 21% VAT, the pre-tax price isn't 121 minus 21%; it's 121 ÷ 1.21 = €100. Working backwards through a percentage is the single most common place people get percentages wrong.
Subtract the old value from the new, divide by the old value, multiply by 100: (new − old) ÷ old × 100. A salary going from ₹8,00,000 to ₹9,20,000 is a 15% raise. Rent rising from $1,600 to $1,800 is a 12.5% increase. Note the asymmetry trap: a stock that falls from $100 to $80 has dropped 20%, but climbing back from $80 to $100 is a 25% gain — because the base changed. A 50% loss needs a 100% gain to break even. This is why "it went down X% then up X%" never returns you to the start.
Multiply by (1 + rate) to increase or (1 − rate) to decrease: 500 increased by 10% = 500 × 1.10 = 550; decreased, 500 × 0.90 = 450. Chaining matters here: two successive 10% increases aren't 20% — they're 1.10 × 1.10 = 21%. The same applies to inflation compounding year over year, or a price that's marked up 30% and then discounted 30% (you end up at 91% of the original, not 100%).
When neither value is the "original" — comparing prices at two shops, or output of two machines — percentage change is the wrong tool because there's no natural base. Percentage difference solves this by measuring against the average of the two values: |a − b| ÷ ((a + b) ÷ 2) × 100. Comparing 26 and 14: the gap is 12, the average is 20, so the percentage difference is 60%. It's symmetric — you get the same answer whichever number you enter first.
If a central bank rate moves from 5% to 7%, that's a rise of 2 percentage points, but a 40% relative increase in the rate itself (2 ÷ 5 × 100). Headlines routinely blur the two — "unemployment up 3%" could mean either, and the difference between 10% → 10.3% and 10% → 13% is enormous. When precision matters, say "points" for absolute changes in a rate and "percent" for relative ones.
Beyond the asymmetry and chaining traps above: percentages of different bases can't be added (a 10% discount on shoes plus a 10% discount on a jacket isn't "20% off the order"); an average of percentages is only valid when the underlying bases are equal; and "up to 70% off" legally means at least one item, somewhere, is 70% off. Finally, tiny bases produce dramatic-sounding percentages — going from 2 users to 4 is "100% growth," which is why early-stage statistics deserve a skeptical read of the absolute numbers behind them.
Mode 1 covers tips (US), VAT/GST additions (Europe, India), commissions, and interest for one period. Mode 2 covers exam marks, attendance, conversion rates, and body-fat or budget shares. Mode 3 covers back-calculating pre-tax prices, deposits, and "the sale price is $68 after 15% off — what was it originally?" Mode 4 covers salary changes, price and market moves, and year-over-year growth. Mode 5 covers markups, raises, shrinkage, and inflation adjustments. Mode 6 covers side-by-side comparisons with no before/after. If you're specifically working with sale prices, the Discount Calculator adds currency handling and reverse-price modes; for tax-inclusive pricing, the GST / VAT Calculator handles country-specific rates.
A laptop lists at $1,200 in a Black Friday sale at 25% off. Mode 1: the discount is 1,200 × 25 ÷ 100 = $300, so you pay $900. Sales tax of 8% applies at checkout — Mode 5: 900 × 1.08 = $972 out the door. A month later the same model is back at $1,200 — Mode 4 says the price rose (1,200 − 900) ÷ 900 × 100 = 33.3% from what you paid, even though the sale was "only" 25% off. Same dollars, different bases.