Subtracting Decimals — Definition, Formula & Examples
Subtracting decimals is finding the difference between two numbers that have digits after the decimal point. You line up the decimal points, add placeholder zeros if needed, then subtract column by column just like whole numbers.
Decimal subtraction is the operation of computing the difference of two decimal numbers by aligning their decimal points vertically, padding with trailing zeros so both numbers have the same number of decimal places, and performing place-value subtraction from right to left with regrouping as necessary.
How It Works
Write the two numbers in a column so the decimal points are directly above each other. If one number has fewer decimal places, add zeros to the right until both numbers are the same length. Subtract each column starting from the rightmost digit, borrowing from the next column when the top digit is smaller. Bring the decimal point straight down into your answer.
Worked Example
Problem: Subtract 5.3 − 2.87.
Line up decimal points and pad with zeros: Write 5.3 as 5.30 so both numbers have two decimal places.
Subtract the hundredths column: 0 is less than 7, so borrow 1 from the tenths column. 10 − 7 = 3.
Subtract the tenths column: After borrowing, the tenths digit is now 2. Since 2 is less than 8, borrow from the ones column. 12 − 8 = 4.
Subtract the ones column: After borrowing, the ones digit is now 4. 4 − 2 = 2. Bring down the decimal point.
Answer: 2.43
Why It Matters
Subtracting decimals comes up whenever you calculate change from a purchase, measure differences in length or weight, or compare times in a race. Mastering it also prepares you for working with negative numbers and algebra in later grades.
Common Mistakes
Mistake: Forgetting to add placeholder zeros, which causes digits to be misaligned (e.g., subtracting 5.3 − 2.87 as if it were 53 − 287 or lining up the 3 with the 7).
Correction: Always write 5.3 as 5.30 first, so both numbers have the same number of decimal places. Then subtract column by column with the decimal points aligned.