Percent Calculator
Shopping, salary negotiation, taxes, stats — every percent calculation. Live result + delta.
Result
Result
7,500
What this tool does
The percent calculator handles the five most common percent operations on one screen — B% of A (discount/portion), A increased by B%, A decreased by B%, change rate from A to B, and reverse calculation when the result of a B% increase equals A. Use it for shopping discounts, VAT separation, salary raises, profit margins, and investment returns.
Who uses this
- Shopping: actual paid amount after a 20% discount
- Salary: change rate from last year's KRW 50M to this year's KRW 55M (10%)
- VAT split: separate KRW 110K (VAT-inclusive) into KRW 100K supply + KRW 10K VAT
- Margin: cost KRW 10K → sale KRW 15K (50% markup, 33.3% margin)
- Investment: KRW 100M invested → KRW 120M returned = 20% gain
How to use
- 1Pick one of the five modes: B% of A, A increased by B%, A decreased by B%, change rate from A to B, or reverse (find original from increased value).
- 2Enter the two values required by the chosen mode. The result updates instantly — no Calculate button needed.
- 3Preset buttons for VAT (10%) and common discounts (10/20/30/50%) speed up common cases.
Five mode formulas
1) B% of A : A × B/100 Example: 20% of 50,000 = 10,000 2) A increased by B%: A × (1 + B/100) Example: 30,000 + 10% = 33,000 3) A decreased by B%: A × (1 − B/100) Example: 30,000 − 10% = 27,000 4) A → B change rate: (B − A) / A × 100 Example: 100 → 130 = +30% 5) Reverse from B% increase: A / (1 + B/100) Example: VAT-inclusive 11,000 → 11,000 / 1.10 = 10,000 (supply price)
Real examples
Example 1: 30% off KRW 89,000
Decreased mode → A=89,000, B=30. Result = 89,000 × 0.70 = 62,300. Discount amount = 26,700.
Example 2: Salary KRW 50M → KRW 54M raise rate
Change rate mode → A=50,000,000, B=54,000,000. Rate = (54M − 50M) / 50M × 100 = 8%. Net pay differs after taxes and insurance — check separately.
Example 3: VAT-inclusive estimate KRW 2.2M → split
Reverse mode → A=2,200,000, B=10. Supply = 2,200,000 / 1.10 = 2,000,000. VAT = 200,000.
Frequently asked questions
Does +10% then −10% return to the original?+
No. 100 → +10% = 110 → −10% = 99. A 1% loss occurs because the percentages apply to different base values (100 vs 110).
How do I split VAT (10%)?+
Inclusive ÷ 1.1 gives the supply price; the difference is VAT. Example: 11,000 inclusive → 10,000 supply + 1,000 VAT. Multiplying inclusive by 10% is the wrong calculation.
Are margin and markup the same?+
No. Cost 10K → sale 15K means 50% markup (against cost) but 33.3% margin (against sale price). Markup measures cost-to-price; margin measures profit-to-price.
Is the percent calculation the same as compound vs simple interest?+
Simple is straight addition each period; compound applies the rate to the new balance each period. Single-rate increases here are simple. For multi-period returns, use the compound interest calculator.
I see rounding differences in discount calculations+
The calculator shows two decimals. Real charges round to the nearest won (by card-network policy), so 1-2 won differences can appear. Verify against the actual receipt for large amounts.
Can the change rate be negative?+
Yes. 100 → 80 = (80−100)/100 = −20%. The calculator shows signed change rates automatically.
Cautions
- •+B% then −B% does not return to the original (100 → 110 → 99).
- •Split VAT via 'inclusive ÷ 1.1', not 'inclusive × 10%'.
- •Markup (vs cost) and margin (vs sale price) are different ratios.
- •Card-network and tax-office rounding rules may differ — verify on actual receipts for large amounts.
Last reviewed: 2026-05-23