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The What's My Number campaign has been credited with spurring competition between electricity retailers.
Last year, 388,000 people switched retail companies after calculating it would save them money to do so.
Collectively they stood to save about $8.7 million on their power bills.
A further 98,550 switched in the first three months of this year.
That had spurred retailers to offer customers better plans and choices, Electricity Authority chief executive Carl Hansen said in a statement.
"Due to increased competition, there is now a new average savings number of $165 [per household annually] compared to $150 in 2011."
Statistics supplied by the authority to the Otago Daily Times yesterday showed the retailers who dominated the market before the campaign gathered momentum have been the biggest losers.
In Otago, Contact Energy lost almost half its customers between 2008 and the end of last year, while TrustPower's customer base dropped 3%.
The companies to gain customers in that period were Genesis (11%), Powershop (2.5%), and Meridian (2%).
In Southland, the loser was again Contact (22%) and the winners TrustPower (10%), Meridian (7%), Pulse (5%) and Genesis (2%).
The authority does not keep statistics on the number of Otago people using the calculator or switching companies.
A spokeswoman yesterday said work had begun to provide regular regional breakdowns soon.