How is a Peru RUC check digit calculated?

Multiply the first 10 digits by the weights 5, 4, 3, 2, 7, 6, 5, 4, 3, 2 and sum the products. Compute 11 minus (sum mod 11). If the result is 10 the check digit is 0; if it is 11 the check digit is 1; otherwise the check digit is that result. It must equal the 11th digit.

How many digits is a RUC?

A RUC is exactly 11 digits. The first two digits are a type prefix (10 and 15 for individuals, 17 for non-domiciled, 20 for legal entities). The last digit is the modulo-11 check digit.

Does a valid check digit mean the company is active?

No. A valid check digit confirms the RUC is internally well-formed. It does not confirm the taxpayer is registered or in an active state at SUNAT. Use SUNAT's official consulta RUC service to confirm status.

Why does my RUC fail validation?

A failed check almost always means a digit was mistyped or transposed, or the number is not 11 digits long. Re-check the digits against the source comprobante de pago or DNI-derived RUC.

Is my RUC sent anywhere?

No. The entire calculation runs locally in your browser. The RUC never leaves your device and no request is made to SUNAT.

Peru RUC Validator — Gera Tools

A RUC (Registro Único de Contribuyentes) is the 11-digit tax identification number that Peru’s tax authority, SUNAT, assigns to every taxpayer — individuals and companies alike. It appears on every comprobante de pago (electronic invoice, boleta, factura) and is required for electronic invoicing. This validator checks that an RUC is internally well-formed using SUNAT’s official modulo-11 check digit, entirely in your browser.

How it works

SUNAT computes the 11th digit (the check digit) from the first 10 digits using a weighted modulo-11 algorithm:

Strip spaces and dashes so you have 11 digits.
Multiply each of the first 10 digits by the fixed weights 5, 4, 3, 2, 7, 6, 5, 4, 3, 2.
Add the 10 products together to get the weighted sum.
Compute 11 - (sum mod 11).
If that value is 10, the check digit is 0; if it is 11, the check digit is 1; otherwise it is the value itself.
The RUC is valid if the computed check digit equals the actual 11th digit.

The tool also verifies the type prefix: valid leading pairs are 10 and 15 (natural persons), 17 (non-domiciled), and 20 (legal entities).

Example

Validate 20100066603. The first 10 digits are 2 0 1 0 0 0 6 6 6 0 with weights 5 4 3 2 7 6 5 4 3 2:

(2×5)+(0×4)+(1×3)+(0×2)+(0×7)+(0×6)+(6×5)+(6×4)+(6×3)+(0×2)
= 10 + 0 + 3 + 0 + 0 + 0 + 30 + 24 + 18 + 0 = 85

85 mod 11 = 8, so 11 - 8 = 3. The expected check digit is 3, which matches the 11th digit, so the RUC is valid.

Notes

A valid check digit confirms the RUC is consistent, not that the taxpayer is registered or active — use SUNAT’s official consulta RUC for that. The prefix check is informational: a number can pass the modulo-11 test with an unusual prefix. Everything runs locally, so your RUC never leaves your device.