Digit Sum Calculator

A digit sum is the result of adding all the individual digits of a number together, ignoring their place values. For example, the digit sum of 567 is 5 + 6 + 7 = 18. Digit sums are used in divisibility checks, numerology, and various math puzzles.

Simply write out each digit of the number and add them all together. For 1234, you compute 1 + 2 + 3 + 4 = 10. Our calculator does this automatically for any number you enter, no matter how large.

An iterated digit sum (also called a digital root) is calculated by repeatedly summing the digits of a number until you reach a single-digit result. For example, 1234 → 1+2+3+4 = 10 → 1+0 = 1. The final single-digit result is the digital root.

An alternating digit sum alternately adds and subtracts the digits from left to right: z1 − z2 + z3 − z4 + z5... For 1234, that would be 1 − 2 + 3 − 4 = −2. Alternating digit sums are used for the divisibility rule for 11.

A Harshad number (or Niven number) is an integer that is divisible by its own digit sum. For example, 18 has a digit sum of 9, and 18 ÷ 9 = 2, so 18 is a Harshad number. The name 'Harshad' comes from Sanskrit, meaning 'great joy'.

A digit is any single symbol used to represent numbers — in the decimal system, these are 0 through 9. A number is a value composed of one or more digits. For example, 345 is a number made up of three digits: 3, 4, and 5.

If the digit sum of a number is divisible by 3, then the original number is also divisible by 3. Similarly, if the digit sum is divisible by 9, the original number is divisible by 9. These rules make mental divisibility checks much faster.

The sum of all individual digits of every number from 1 to 100 is 901. This accounts for counting the digits 0–9 across all numbers in that range, weighted by how many times each digit appears.