Zimbabwe ID Check Letter Explained
The check letter is one of the simplest ways to test whether a Zimbabwe ID number is internally consistent. This guide explains the logic behind it.
Quick answer
The check letter is calculated from the registration code and sequence number using the mod-23 rule. If the result does not match the letter printed in the ID number, the number should be treated as invalid or mistyped.
Position: the check letter appears before the final two-digit district code.
What mod-23 means
The mod-23 calculation is the rule used to produce the check letter. In simple terms, it works like this:
- combine the registration code and sequence number
- divide the combined value by 23
- take the remainder
- map that remainder to a letter
Worked example
Here is a worked example for ID number 12-345678-A-90:
Step 1: Extract registration code and sequence number
Registration code: 12
Sequence number: 345678
Step 2: Combine them
Combined value: 12345678
Step 3: Divide by 23
12345678 ÷ 23 = 536768 remainder 1
Step 4: Map remainder to letter
Remainder 1 = A
Letter mapping table
The table below shows how remainders map to letters. The letters I and O are not used.
| Remainder | Letter | Remainder | Letter |
|---|---|---|---|
| 0 | Z | 12 | M |
| 1 | A | 13 | N |
| 2 | B | 14 | P |
| 3 | C | 15 | Q |
| 4 | D | 16 | R |
| 5 | E | 17 | S |
| 6 | F | 18 | T |
| 7 | G | 19 | V |
| 8 | H | 20 | W |
| 9 | J | 21 | X |
| 10 | K | 22 | Y |
| 11 | L | - | - |
Why I and O are excluded
The letters I and O are excluded because they can easily be confused with the numbers 1 and 0.
Why the check letter matters
The check-letter system helps because:
- Consistency check: changed digits usually break the letter match.
- Error detection: many typing mistakes are caught quickly.
- Simple review: the rule can be tested automatically by a validator.
If the letter is wrong
If an ID has an incorrect check letter, it usually means one of the following:
- the number was typed incorrectly
- the number was altered
- the record needs a closer manual review
Use the validator
Instead of calculating the letter by hand each time, use the validator to:
- check the number format
- calculate the mod-23 result
- compare it with the given letter
- review the result in one place
Check the letter automatically
Open the validator to test the ID format, the check letter, and the district code together.
Open the validator