A first class stamp will increase by 1p to 65p and second class by 1p to 56p when the changes are introduced on March 27.
Royal Mail said the changes are needed "to help ensure the sustainability of the Universal Postal Service".
The cost of large letter first class stamps will also rise by 2p to 98p, and large letter second class stamps will increase by 1p to 76p.
The latest increase follows a previous 1p rise for both first class and second class stamps in March 2016.
Royal Mail defended the increases, saying that the price of UK stamps remain among the best in Europe when compared with their counterparts.
The group said: "Royal Mail understands how hard it is for many companies and households in the current economic environment.
"For that reason, we have considered any pricing changes very carefully and have sought to minimise any impact on our customers."
The average European cost of a first class letter is 87p and the average European cost of a second class letter is 67p, compared with 65p and 56p respectively in the UK, Royal Mail said.