If you prefer not to use third-party calculators, try these official routes:

Free Blaupunkt code calculators are small software programs (often .exe files) or web-based scripts. They use a mathematical algorithm to convert the radio's serial number into the unlock code.

If you prefer using your phone, several independent apps on the Google Play Store can calculate codes: Radio Code Generator Unlocker - Apps on Google Play

You have 3 attempts. After 3 wrong codes, the radio will display "WAIT" or "SAFE" and lock you out for 1 hour (or 24 hours on newer models). Unplugging the battery will not reset the attempt counter.