The 2p price rise in the cost of first and second class stamps has now taken effect.
A first-class stamp now costs 67p and a second-class stamp now costs 58p, under the price rises that came into force on Monday.
Stamps bought before the price rise can still be used without any need to top-up the cost.
Royal Mail said the squeeze on consumer finances was considered when setting the new price.
But it added that the price rise was needed to maintain the universal postal service, which means that the price of a stamp is the same irrespective of where in the UK the letter is sent from and to.
If the price of a first-class stamp had risen in line with inflation since 1989, it would now cost 41p.
If the price of a second-class stamp had risen in line with inflation since 1989, it would now cost 31p.
The price of a first-class stamp for a large letter has risen by 3p to £1.01. A second-class stamp for a large letter has also risen in cost by 3p to 79p.
All the changes were first announced in February.