How it works
The algorithm converts each of the 10 NMI characters to its ASCII code value. Characters at even positions (2nd, 4th, 6th, 8th, 10th — zero-indexed odd positions) are multiplied by 2. The individual digits of every value are summed. The check digit is (10 − (sum mod 10)) mod 10.
Worked example
NMI: 4123456789. ASCII values: 52, 49, 50, 51, 52, 53, 54, 55, 56, 57. Double even-positioned: 52, 98, 50, 102, 52, 106, 54, 110, 56, 114. Sum digits: 5+2 + 9+8 + 5+0 + 1+0+2 + 5+2 + 1+0+6 + 5+4 + 1+1+0 + 5+6 + 1+1+4 = 84. Check digit: (10 − 84 mod 10) mod 10 = (10 − 4) mod 10 = 6. Full NMI with check digit: 41234567896.
What is an NMI?
A National Metering Identifier (NMI) is a unique 10-character alphanumeric code assigned to every electricity (and gas) metering point in Australia. It identifies the connection point, not the meter itself. The 11th character is a check digit used to detect transcription errors.
Where do I find my NMI?
Your NMI appears on your electricity bill, usually near the top or in the supply/meter details section. It is also on your meter, or you can ask your retailer or distributor. It is 10 or 11 characters long (letters and digits).
Assumptions & limitations
Uses the standard AEMO NMI checksum algorithm. The NMI must be exactly 10 alphanumeric characters (letters A–Z and digits 0–9). The check digit is always a single digit 0–9.