Percentage Calculator: % Of, % Change, Discount and Reverse
Percentage of a number
42
15% of 280 = 15 ÷ 100 × 280 = 42
What percentage is it?
75%
45 ÷ 60 × 100 = 75%. Scored 45 out of 60 in a test? That is 75%.
Percentage increase or decrease
+10.42%
(2,650 − 2,400) ÷ 2,400 × 100 = 10.4167%, a rise of 250. A pay rise from S$2,400 to S$2,650 is a 10.42% increase.
Discount and sale price
S$90.30
S$129.00 × (1 − 30%) = S$90.30 = S$90.30. You save S$38.70.
Reverse percentage (find the original)
100
109 ÷ (1 + 9%) = 109 ÷ 1.09 = 100. Check: 100 + 9% = 109. S$109 including 9% GST was S$100 before GST.
GST-registered shops in Singapore must show prices with GST included, so a shelf or online price is usually already GST-inclusive. Pick “before GST” for B2B quotes and price lists marked “+GST”.
How this works
A percentage is a number out of 100. X% of Y is X ÷ 100 × Y, so 15% of 280 is 42. To find what percentage A is of B, divide A by B and multiply by 100: 45 out of 60 is 75%.
Percentage change compares the difference with the starting value: (new − old) ÷ old × 100. A pay rise from S$2,400 to S$2,650 is (250 ÷ 2,400) × 100 = 10.42%. Going back from S$2,650 to S$2,400 is a 9.43% fall, because the starting value is now larger.
A discount multiplies the price by (1 − discount). Stacked discounts multiply too, so 30% off then an extra 10% off is 37% off in total, not 40%. GST-registered businesses in Singapore must display prices with GST included; when a price is quoted before GST, the 9% is added after the discount.
A reverse percentage finds the original from the result: divide by (1 + rate) after an increase or (1 − rate) after a decrease. S$109 including 9% GST was S$100 before GST; a S$56 item after 20% off was S$70 before the sale.
FAQs
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. From S$2,400 to S$2,650 is (2,650 − 2,400) ÷ 2,400 × 100 = 10.42%.
How do I work out 30% off a price?
Multiply the price by 0.70. A S$129 item at 30% off is S$90.30, a saving of S$38.70. If the price is before GST, add 9% afterwards: S$98.43.
Is 30% off plus an extra 10% off the same as 40% off?
No. The extra 10% applies to the already-reduced price, so the total is 37% off. On S$129 that is S$81.27, not S$77.40.
How do I find the original price before a percentage was added?
Divide by 1 plus the percentage. A S$109 price including 9% GST was S$109 ÷ 1.09 = S$100 before GST. After a 20% discount, divide by 0.80 instead: S$56 was S$70.
What percentage is 45 out of 60?
75%. Divide 45 by 60 to get 0.75, then multiply by 100.