Just a PSA, the IRS recently instituted some kind of AI algorithm that is re-flagging a lot of things that have already been resolved... a friend got a bill for $1500 which they had earlier sent a letter of apology for. He doesn't actually owe anything, it's just the glitchy algorithm sending the old bill out again.

If you don't understand why you owe more, don't just give up and pay it. The IRS can make mistakes too.

Years ago they actually sent me a check because they thought I should have taken a deduction that I didn't. I didn't want to get on a gotcha list, so I sent back a letter explaining that the deduction was not proper for my situation, and they responded that if that was the case, I needed to file an amended return. That was way more energy than I wanted to spend on this issue, so I just ignored the check... until the next year, when they mailed me another one with a tartly-worded form letter about the importance of promptly depositing it, and again the year after. At that point I figured if Uncle Sam is that desperate for me to take the money I'd indulge him. At this point I'm well past the statute of repose for any potential issues that created, so I think I'm in the clear, but I guess we'll see.

If your itemized deductions are higher than your standardized deduction, you're likely in a fairly high income bracket and can have a professional do it for you.