Multiply, divide, add or subtract decimals and see exactly how it's done on paper, step by step. Answers are exact, with no rounding errors.
How to multiply decimals
- Ignore the decimal points and multiply the whole numbers. For 2.5 × 0.34, work out 25 × 34 = 850.
- Count the decimal places in both numbers together: 2.5 has 1 and 0.34 has 2, so 3 in all.
- Put the point that many places from the right: 850 becomes 0.850, which is 0.85.
How to divide decimals
Move the decimal point in both numbers the same number of places until you're dividing by a whole number, then divide as usual. 4.2 ÷ 0.06 becomes 420 ÷ 6 = 70. Moving both points together doesn't change the answer.
How to add and subtract decimals
Line up the decimal points, adding zeros so both numbers have the same number of decimal places, then add or subtract like whole numbers. 3.7 + 12.45 is 3.70 + 12.45 = 16.15.
Why exact matters
Many calculators work in binary and show 0.1 + 0.2 as 0.30000000000000004. Calcist works with the digits you typed, so 0.1 + 0.2 is exactly 0.3.
How we checked this
Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:
- 2.5 × 0.34 = 0.85 ✓
- 4.2 ÷ 0.06 = 70 ✓
- 3.7 + 12.45 = 16.15 ✓
- 0.1 + 0.2 = 0.3 exactly ✓
- −1.5 × 0.2 = −0.3 ✓
Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.
Questions people ask
How do you multiply decimals?
Multiply as if there were no decimal points, then count the decimal places in both numbers and put that many in the answer. 1.2 × 0.3: 12 × 3 = 36, two decimal places, so 0.36.
How do you multiply decimals by decimals?
The same way: 0.5 × 0.5 is 5 × 5 = 25 with two decimal places, so 0.25.
How do you divide by a decimal?
Move both decimal points right until the number you divide by is whole. 9 ÷ 0.3 becomes 90 ÷ 3 = 30.