Rol Único Tributario / Rol Único Nacional
Chile · Individuals and companies
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What this check does — and what it cannot do
This tool checks the number's structure and its check digit, using the published algorithm for that document. A number that passes is well formed: it is arithmetically consistent and could have been issued.
It cannot tell you whether the number was actually issued, whether it is active, or who it belongs to. Only the issuing tax authority can confirm that, through its own lookup service. Treat a passing result as "worth submitting", never as proof of identity.
The generator produces numbers that satisfy the same checksum, for filling forms while developing and testing software. They are arithmetic, not records: they are not drawn from any register and do not correspond to a real holder. No generator is offered for the US Social Security Number.
One RUT in eleven ends in a letter, and that breaks numeric-only systems
The Chilean RUT ends in a check digit computed mod 11. Eleven possible remainders have to fit into ten digits, so one case overflows and is written as K. That single letter is why storing a RUT as an integer quietly corrupts about 9% of your records.
How it works
- Recomputes the check digit from the body using the repeating 2–7 weight cycle and compares it to the one supplied.
- Handles K correctly, which is the case naive validators and integer columns get wrong.
- Accepts the number with or without dots and hyphen, since both forms circulate.
multiply the body right-to-left by weights 2, 3, 4, 5, 6, 7 then repeat from 2 sum the products check = 11 − (sum mod 11) 11 → 0 10 → K anything else → itself
Worked example
Deriving the check digit for the body 12345678, and finding one that yields K.
- weights applied right-to-left: 2, 3, 4, 5, 6, 7, 2, 3
- the weighted sum reduces mod 11
- 11 − remainder gives 5, so the RUT is 12.345.678-5
- body 10000013 instead produces remainder 1
- 11 − 1 = 10, which is written K: 10.000.013-K
Sampling 100,000 consecutive bodies, 9,090 of them — 9.09%, almost exactly 1 in 11 — require a K. It is not an edge case; it is a ninth of the population.
Reading the result
- Store a RUT as text, never as a number. An integer column cannot hold K, so those records are either rejected at insert or silently mangled, and the failure shows up much later as customers who cannot log in.
- The K is conventionally uppercase, but lowercase k circulates widely in user input. Normalise case before comparing, or roughly a ninth of your valid RUTs will fail validation for cosmetic reasons.
- The same person's RUT and RUN are the same number — RUT for tax purposes, RUN for identity. Systems that model them as separate fields end up storing the identical value twice and letting the copies drift.
- As with every checksum, a passing RUT means the digits are consistent, not that the number was issued. Only the Servicio de Impuestos Internos can confirm that.
Common questions
- Why does the check digit use letters at all?
- Because mod 11 produces eleven possible values and only ten fit in a single digit. Chile writes the eleventh as K rather than lengthening every RUT by a character. Other mod-11 schemes solve it differently — the Brazilian CPF maps the overflow to 0.
- How often does K actually come up?
- About one RUT in eleven, or 9.09% measured over a hundred thousand consecutive numbers. Any system handling Chilean identifiers at scale will encounter it within the first dozen records.