I'd recommend people use my much more advanced Postage Pro UK 2018 instead of this app, but I've kept it updated since it still has a surprising number of users.
Stamp prices updated for 26th March 2018, next expected change for 1st and 2nd class stamps is late March / early April 2019.
Do you use 1st and 2nd class stamps to send heavier letters? With Many Stamps it's easy, just tell it the cost, and it tells you the easiest way to reach that value using 1st and 2nd class stamps (see screenshots for details).
Check out my other apps if you often send postage, they will make your life easier.
Please email firstname.lastname@example.org if you have any questions or suggestions.