ID checksum and 15-digit vs 18-digit numbers
Why the last digit exists, and how older 15-digit numbers map to 18-digit ones.
The final character is a checksum over the first 17 digits under the national standard, catching typos.
Older 15-digit numbers omit the century digit and checksum; this tool can upgrade them for parsing.
A valid checksum only means the number is self-consistent — not that a real person holds it.
Avoid entering other people’s full IDs on untrusted sites; this tool keeps processing local.