The price of a first-class stamp has risen to £1.25 from £1.10 – the third increase in 18 months.
Royal Mail has blamed the rise on increasing cost pressures and the tough economic environment.
The move has been criticised, with charity Citizens Advice saying that regulator Ofcom should hold the firm to account over “rocketing prices” while households struggle with rising costs.
However, Ofcom said pricing “flexibility” was needed to ensure the postal service remained viable.
The price of a second-class stamp remains unchanged at 75p.
