Digit Sum & Digital Root Calculator
Add up every digit of a whole number and reduce it to a single-digit digital root.
Digital root: 9
How does this calculator work?
The digit sum adds every digit of a number; the digital root keeps summing those digits until one digit remains. Enter any non-negative whole number to get its digit sum, digital root, and digit count instantly. The digital root equals 1 + ((digit sum − 1) mod 9), or 0 when the number is 0.
Formula
How this is calculated
Enter any non-negative whole number. Because the value is read as text, the calculator handles numbers far larger than a standard 64-bit integer without losing precision. Leading zeros are ignored when counting digits, so 007 is treated as 7.
The digit sum is computed by adding the numeric value of each character: for 1234 it is 1 + 2 + 3 + 4 = 10. The digital root is the result of repeatedly summing digits until a single digit remains (10 → 1). Rather than looping, it is found directly with the congruence formula: the digital root equals 0 when the number is 0, and otherwise 1 + ((s − 1) mod 9), where s is the digit sum. This works because a number is congruent to its digit sum modulo 9.
The digit count is simply the number of digits after removing leading zeros. Inputs containing signs, decimals, spaces, or letters are rejected, since digit summation is defined here for non-negative integers only.
Frequently asked questions
A digital root is the single-digit value obtained by repeatedly adding the digits of a number until only one digit is left. For 9875, 9+8+7+5 = 29, then 2+9 = 11, then 1+1 = 2.
Every number leaves the same remainder when divided by 9 as the sum of its digits does. The digital root is that remainder, except multiples of 9 give a digital root of 9 instead of 0.
Yes. The number is processed as text one digit at a time, so it works for numbers with hundreds of digits without floating-point rounding errors.
Also known as
TG we-Calculate Editorial Team. (2026). Digit Sum & Digital Root Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/digit-sum-calculator
TG we-Calculate Editorial Team. "Digit Sum & Digital Root Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/digit-sum-calculator.
TG we-Calculate Editorial Team, "Digit Sum & Digital Root Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/digit-sum-calculator
@misc{wecalculate_digit_sum_calculator, title = {Digit Sum & Digital Root Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/digit-sum-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?