Yes, their value will increase when the cost of postage goes up. And you will pay the current cost for stamps at the post office.
Forever
Yes. That's why it's called a "forever stamp". It will remain sufficient postage for a first-class letter indefinitely regardless of future postage increases.
The forever stamp eliminates the need to print new stamps before a rate increase goes into effect. The stamp is still valid of that first ounce of postage.
Yes, you can use a Forever stamp on a postcard, but it's overpaying for postage.
Yes, it is non-denominated.
As of 2016, the rate dropped to 47 cents.
A three cent stamp will be good forever for US postage. Every US stamp issued since 1861 is valid for postage.
The postage stamp that had the word LOVE and a single pink rose on it, is a forever stamp. There was also one that had a value of .25 cents.
Use the postage calculator on the USPS website to figure out the first class postage due for the weight of your envelope, then divide by the current first class stamp price, then round up to determine how many forever stamps to use. As of 4/2009, forever stamps are worth $0.42 each, but their value will increase to $0.44 next month when postage goes up.
The Forever stamp is not to be used for postage overseas. If you are mailing a letter to a soldier, and using the APO box, normal rates apply. You would be able to use a Forever stamp for that letter.
A Forever stamp is good for one ounce of First Class Postage inside the US.
Nope. You can always get a forever stamp.