On Monday, 30 April Royal Mail will change its prices.The price of a first-class stamp will go up from 46p to 60p - a 30% increase - and second-class stamps will rise from 36p to 50p.
But the changes are less clear-cut when it comes to packets and parcels.
In some cases, prices will go up by 71%; in other circumstances they could also go down by 11.5%.
At the moment, Royal Mail charges for packets according to how much they weigh.
Anything less than 100g currently costs £1.58 and an item between 501-750g is £3.05.
But from Monday, this system is being replaced by a flat rate.
From then on, anything up to 750g will cost £2.70 and that means an increase of 71% for the lightest items.