Digital Root Calculator
Find the digital root — the digit sum repeated to one digit.
What is Digital Root?
The digital root is what is left when the digits are summed, and summed again, until a single digit remains: 38 → 11 → 2. For any positive number it equals 1 + (n − 1) mod 9 — 'casting out nines' — which is why a digital root of 9 means exactly 'divisible by 9', and why it is the arithmetic behind the add-the-digits divisibility tricks.
How it works
Each pass sums the digits of the previous result, and the passes are printed as they happen (38 → 3 + 8 = 11 → 1 + 1 = 2), so the two routes to the answer — the loop and the one-step congruence — are both shown and can be seen to agree. The root survives any rearrangement of the digits, which is why 38 and 83 both have root 2.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.