Oh, no. Surely we're not about to tell you that a word you use as often as "often" is often pronounced incorrectly? Well, with apologies, I'm afraid we are. And the explanation isn't even a good one, because what we're about to tell you is probably the opposite of what you think we're going to say.
For some reason - and feel free to check Merriam-Webster on this, because we did - the 't' is silent. It goes against seemingly every rule of pronunciation, but that's the fact. So, whilst saying "off-ten" might feel like the right thing to do, you should be ignoring that 't' and saying "off-en". Even the dictionary recognizes that this is contentious and says so in its listing. What can we say? The rules around pronunciation often don't make sense.