The price of a stamp for a standard domestic letter is to rise to 50c at the start of June, New Zealand Post said today.
The increase is the first since April 2004 when the price rose from 40c to 45c.
Postage on Fastpost domestic letters will rise from 90c to $1 but postage on parcels, bulk mail and international mail will not be affected.
NZ Post's mail chief Peter Fenton said growth in the number of addresses to which it delivers and higher labour costs had made the increases necessary.
However, even at 50c New Zealand's standard letter rate was cheaper than Australia, Britain, Canada and most other developed countries.
Fenton said 45c stamps will be accepted until June 1. After that customers could use 5c stamps to top up postage until stocks of old stamps run out.
Last month NZ Post chief executive John Allen said the volume of domestic letters handled by his company was falling at the fastest rate in six years.
Domestic letter volumes have fallen by about 2.9 per cent in the last year having fallen by an average of 1 per cent annually over recent years.
Nevertheless NZ Post still believes its domestic letters business has a strong future and is in the process of investing $80 million on new mail sorting equipment and mail sorting centres.
Even at 50 cents it cost less to send a standard letter in this country than in Australia, Britain, Canada and most of the other OECD countries, Mr Fenton said.
By comparison, Australia's standard postage rate was the equivalent of 56 cents in New Zealand currency, Britain's was 65 cents; Canada's 66 cents; Ireland's 89 cents; Germany's $1.02; and Norway's $1.49.