The price of a first-class stamp will break through the 40p barrier in April, Royal Mail has confirmed.
First and second-class stamps will rise by 2p to 41p and 32p respectively on 6 April 2010, the company said.
The move was expected, with regulator Postcomm announcing in September that it had given approval for stamp price increases in 2010.
However, the cost of a first-class stamp will not go up as much as the 3p rise that the regulator had approved.
Postcomm previously said Royal Mail needed the extra funding to compensate for the continuing decline in mail volumes.
Customer body Consumer Focus said it was disappointed at the rise but "reluctantly accepted" that it was needed, adding that customers "can't keep on footing the bill".
"Unless Royal Mail begin to deliver efficiencies through their modernisation programme and better industrial relations then consumers will rightly start to lose patience with Royal Mail," said Robert Hammond, postal expert at Consumer Focus.