How this calculation works
A whole number and its digit sum leave the same remainder modulo 9 because each power of ten leaves remainder 1.
THE FORMULA
S = d₁ + d₂ + … + dₖA worked example
For 582, add 5 + 8 + 2 to get 15.
Good to know
The digit sum can have more than one digit.
Reference: OpenStax Prealgebra (opens in a new tab) ↗
Read the result
Add the decimal digits in one pass, which is useful when checking divisibility by 3 or 9.
The primary result is labeled “Sum of digits”. Keep the input definitions in view when comparing this result with another method.
Try a related calculation
The digit sum can have more than one digit.
For a related exercise, try the fraction calculator.
A few questions, answered
How can I check the default inputs by hand?
For 582, add 5 + 8 + 2 to get 15.
Which rule does this calculator apply?
S = d₁ + d₂ + … + dₖ