Digit Sum CalculatorFree online math calculator — instant results, no sign-up
Calculate the sum of an integer's decimal digits.
Sign in to save results and favorites.
About the Digit Sum Calculator
The Digit Sum Calculator adds the decimal digits of an integer to produce a single total. For the default input 12345, it adds 1 + 2 + 3 + 4 + 5 and returns 15. It calculates the digit sum once, rather than repeatedly adding digits until only one digit remains.
- Integer
- The whole number whose decimal digits will be added, with a default of 12345 and no measurement units.
Formula and method
S = ∑(i = 1 to k) d_i; for n = 12345, S = 1 + 2 + 3 + 4 + 5 = 15.
- nThe input integer.
- kThe number of decimal digits in the absolute value of n, counting zero itself as one digit.
- d_iThe digit at position i in the decimal representation of the absolute value of n.
- iThe position index used to visit each digit from 1 through k.
- SThe digit sum returned as the result.
Read the integer's decimal digits, ignoring any sign, and start a running total at zero. Add each digit's numeric value to that total once. For 12345, the digits are 1, 2, 3, 4, and 5, so the final total is 15.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Integer12345
Results
- Result15
How to use the Digit Sum Calculator
- 1Enter the whole number in the Integer field, or leave the default value of 12345.
- 2Check that the entry represents an integer rather than a fraction or a decimal with a fractional part.
- 3Run the calculation to add the decimal digits.
- 4Read the Result row: the default input 12345 produces 15.
Reading your result
The Result row shows the sum of the input integer's decimal digits. For 12345, Result = 15 means its five digits add to 15. This is a unitless total, not the number of digits or a place-value-weighted sum.
Limitations
The calculation assumes base-10 notation and whole-number input. A sign is not a digit, so the digit sum is defined using the integer's absolute value. Leading zeros do not change the sum. Fractions and other number bases are outside this calculation's scope. Very long integers require exact digit handling; the page's maximum supported input length is not specified.
Common questions
Does this calculator keep adding digits until the result has one digit?+
No. It returns the first digit sum. For 12345, the output is 15 and the calculation stops there; repeated digit summation is a separate operation used to find a digital root.
Does rearranging the digits change their sum?+
No. Each digit contributes the same value regardless of its position, so rearranging the digits of 12345 leaves the sum at 15.
How are negative signs and leading zeros treated?+
A negative sign contributes nothing because it is not a digit. Leading zeros also contribute nothing, so neither changes the sum of the remaining digits.
What is the digit sum of zero?+
It is zero: the input contains a single digit whose value is zero.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
You might also like
Scientific Calculator
Full scientific calculator with trig, logs, powers, memory and degree/radian modes.
Fraction Calculator
Add, subtract, multiply and divide fractions.
Percentage Calculator
Percent of a number, what percent, and percent change.
Random Number Generator
Generate random integers in a range.
Percent Error Calculator
Error between an observed and true value.
Exponent Calculator
Raise a base to any power.
Results are estimates for informational purposes and are not financial, medical or legal advice.