Rounding Rule
Round up if the next digit is 5+, otherwise round down.
Formula
Variables
Example
4.7 → 5, 4.3 → 4
How it works
When rounding to a chosen place value, you look at the digit immediately to the right. If that digit is 5, 6, 7, 8, or 9, you increase the digit you are keeping by 1; if it is 0, 1, 2, 3, or 4, you leave it as it is. This works because rounding is a shortcut for choosing the nearest value, and 5 is the midpoint where the number is at least halfway to the next higher place.
When to use it
Use this whenever you need an approximate number that is easier to read, compare, or calculate with, such as in money, measurements, test scores, or estimates. It is especially useful when rounding to the nearest whole number, tenth, or hundred.
Worked example, step by step
Round 18.26 to the nearest whole number. Step 1: Identify the whole-number digit: 18.26 → 18 Step 2: Check the next digit to the right: 2 Step 3: Since 2 is 4 or less, keep the whole-number digit the same Step 4: 18.26 rounded to the nearest whole number = 18
Common mistakes to avoid
- Rounding up whenever the next digit is 5 or more, but forgetting which place you are rounding to
- Looking at the wrong digit instead of the one immediately to the right of the place being rounded
- Changing digits farther left instead of only adjusting the digit being kept
Did You Know?
Banks often use "round half to even" (banker's rounding) to avoid a systematic upward bias when rounding millions of transactions.
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