A letter to Europe will rise to 73p and the rest of the world to 80p. The new rates will be introduced on Tuesday 2 May.
Guernsey Post chief executive Boley Smillie said it had tried to minimise the impact.
'However, some of our costs have increased significantly, such as the price we pay for the onward conveyance and delivery of international mail, and we unfortunately have to reflect these charges in our prices. Overall the changes to our tariffs across business and domestic customers will generate additional revenue of less than 1%.'
The full tariff will be available from Monday 18th April 2017.
