The price of a first class stamp is to rise by 2p to 34p from next April, the Royal Mail has announced.
A new pricing structure for letters was introduced in August
The cost of a second class stamp will also increase, by 1p to 24p. The hikes come after the price of both stamps rose 2p last April.
The cost of larger first class letters of up to 100g will rise 4p to 48p, and bigger second class items by 3p to 40p.
The Royal Mail said the new prices will more closely reflect the "true cost" of its operation.
In August, it introduced a new pricing structure based on the size, weight and thickness of items.
"Stamped mail made a loss of £237m in the 2005-06 financial year, equivalent to 6p on every first and second class stamped letter," said Lorna Clarkson, Royal Mail's director of commercial policy and pricing.
"At the same time, profitable business mail is being targeted by competitors who will handle around 2.5 billion unstamped business items this year."
The price of business post will rise at a lesser rate and discounts will be offered for some services, such as lower weights of franked mail.