A second-class stamp will go up from 36p to 50p - some 5p below the top price allowed by Ofcom.
The regulator has allowed Royal Mail to set the price of first-class and business mail.It claimed the future of the universal service was at "severe risk" without relaxing controls.
The 30% price rise in first-class stamps, and 39% rise for second-class, mark the biggest annual increase in percentage terms since 1975. Ten years ago, a first-class stamp cost 27p, and a second-class cost 19p.
Over the next seven years, the price of second-class stamps will be capped at 55p but this limit could rise with inflation each year.
Royal Mail said that the cost of posting Christmas cards in 2012 will be the same as last year for consumers on Pension Credit and Employment and Support Allowance or Incapacity Benefit.
They will be able to buy up to three books of 12 stamps - 36 stamps in total - in one purchase from any Post Office branch from 6 November until the last posting dates before Christmas. Individuals must provide evidence that they are in receipt of these benefits.
Ofcom said that changes needed to be made to price limits, because the future of the UK's universal, six-day-a-week postal service was "at severe risk" as people switched to using text messages, e-mails, and online messaging.
After consultation, it has now confirmed plans to lift some of the price controls - a move recently backed by a committee of MPs.
The Commons Business Committee did raise concerns about vulnerable customers, and Ofcom said the cap on the cost of second-class mail was designed to protect this group of people.
Shortly after the announcement from Ofcom, Royal Mail announced exactly how much it will charge for stamps from 30 April.
The price of a first-class stamp for a standard letter will go up from 46p to 60p on 30 April
A second-class stamp for a standard letter will go up from 36p to 50p on the same date
A first-class stamp for a large letter weighing up to 100g will rise from 75p to 90p
A large letter sent second-class will cost 69p, rather than 58p
Parcels, franked mail, recorded post, redirection services and PO Box use will also be going up in price