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Sum of Digits Calculator.

Add the decimal digits of an integer and return its digital root.

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Integer

Number must be finite.

Results update automatically as you type.

Use Cases

Check divisibility rules

Use the sum of digits to quickly check if a number is divisible by 3 or 9. If the sum is divisible by 3 or 9, then the original number is too.

Example: For 12345, sum = 15, which is divisible by 3, so 12345 is divisible by 3.

Verify calculations and checksums

Use the digital root to verify arithmetic operations or as a simple checksum for data entry. The digital root of a sum equals the digital root of the sum of the digital roots.

Example: Check 123 + 456 = 579: digital root of 123 is 6, of 456 is 6, sum is 12 -> digital root 3; digital root of 579 is 5+7+9=21 -> 3, matches.

Frequently Asked Questions

What is the sum of digits?: The sum of digits is the result of adding all the individual digits of a number together. For example, for the integer 123, the sum of digits is 1 + 2 + 3 = 6.
What is a digital root?: The digital root is the single-digit value obtained by repeatedly summing the digits of a number until only one digit remains. For instance, the digital root of 123 is 6, and for 456 it is 4+5+6=15, then 1+5=6.
Can I use this calculator for negative integers?: Yes, you can enter a negative integer. The calculator will sum the absolute value of the digits, ignoring the minus sign. For example, the sum of digits of -123 is 6.

Tips & Common Mistakes

Tips

Enter any integer, including negative numbers, and the calculator will ignore the minus sign when summing digits.
The digital root is also known as the 'mod 9' value, except when the sum is 9, then the digital root is 9.
Use the sum of digits to quickly check if a number is divisible by 3 or 9.
For large numbers, the digital root can be found by summing digits repeatedly until a single digit remains.

Common Mistakes to Avoid

Forgetting to ignore the minus sign when entering a negative integer; the calculator handles it automatically.
Confusing the sum of digits with the digital root: the sum is the total of all digits, while the digital root is the single-digit result after repeated summing.
Assuming the digital root of a number is always the same as the remainder when divided by 9; it is, except when the remainder is 0, then the digital root is 9.

Last updated: August 13, 2026

Use Cases

Check divisibility rules

Use the sum of digits to quickly check if a number is divisible by 3 or 9. If the sum is divisible by 3 or 9, then the original number is too.

Example: For 12345, sum = 15, which is divisible by 3, so 12345 is divisible by 3.

Verify calculations and checksums

Use the digital root to verify arithmetic operations or as a simple checksum for data entry. The digital root of a sum equals the digital root of the sum of the digital roots.

Example: Check 123 + 456 = 579: digital root of 123 is 6, of 456 is 6, sum is 12 -> digital root 3; digital root of 579 is 5+7+9=21 -> 3, matches.

Frequently Asked Questions

What is the sum of digits?

The sum of digits is the result of adding all the individual digits of a number together. For example, for the integer 123, the sum of digits is 1 + 2 + 3 = 6.

What is a digital root?

The digital root is the single-digit value obtained by repeatedly summing the digits of a number until only one digit remains. For instance, the digital root of 123 is 6, and for 456 it is 4+5+6=15, then 1+5=6.

Can I use this calculator for negative integers?

Yes, you can enter a negative integer. The calculator will sum the absolute value of the digits, ignoring the minus sign. For example, the sum of digits of -123 is 6.

Tips & Common Mistakes

Tips

Enter any integer, including negative numbers, and the calculator will ignore the minus sign when summing digits.
The digital root is also known as the 'mod 9' value, except when the sum is 9, then the digital root is 9.
Use the sum of digits to quickly check if a number is divisible by 3 or 9.
For large numbers, the digital root can be found by summing digits repeatedly until a single digit remains.

Common Mistakes to Avoid

Forgetting to ignore the minus sign when entering a negative integer; the calculator handles it automatically.
Confusing the sum of digits with the digital root: the sum is the total of all digits, while the digital root is the single-digit result after repeated summing.
Assuming the digital root of a number is always the same as the remainder when divided by 9; it is, except when the remainder is 0, then the digital root is 9.

Use Cases

Check divisibility rules

Use the sum of digits to quickly check if a number is divisible by 3 or 9. If the sum is divisible by 3 or 9, then the original number is too.

Example: For 12345, sum = 15, which is divisible by 3, so 12345 is divisible by 3.

Verify calculations and checksums

Use the digital root to verify arithmetic operations or as a simple checksum for data entry. The digital root of a sum equals the digital root of the sum of the digital roots.

Example: Check 123 + 456 = 579: digital root of 123 is 6, of 456 is 6, sum is 12 -> digital root 3; digital root of 579 is 5+7+9=21 -> 3, matches.

Frequently Asked Questions

What is the sum of digits?

The sum of digits is the result of adding all the individual digits of a number together. For example, for the integer 123, the sum of digits is 1 + 2 + 3 = 6.

What is a digital root?

Can I use this calculator for negative integers?

Yes, you can enter a negative integer. The calculator will sum the absolute value of the digits, ignoring the minus sign. For example, the sum of digits of -123 is 6.

Tips & Common Mistakes

Tips

Enter any integer, including negative numbers, and the calculator will ignore the minus sign when summing digits.
The digital root is also known as the 'mod 9' value, except when the sum is 9, then the digital root is 9.
Use the sum of digits to quickly check if a number is divisible by 3 or 9.
For large numbers, the digital root can be found by summing digits repeatedly until a single digit remains.

Common Mistakes to Avoid

Forgetting to ignore the minus sign when entering a negative integer; the calculator handles it automatically.
Confusing the sum of digits with the digital root: the sum is the total of all digits, while the digital root is the single-digit result after repeated summing.
Assuming the digital root of a number is always the same as the remainder when divided by 9; it is, except when the remainder is 0, then the digital root is 9.