you have to guess and if you get it wrong you go to jail for a long time
1) only if you’re lying on purpose to hide taxable income or claim deductions you don’t qualify for (like, don’t lie and tell the IRS you have a kid when you don’t). If you are wrong THEY WILL LET YOU KNOW AND SEND YOU A BILL. (Or if you’re wrong in the other way, they send you a check) Don’t stress about this as long as you’re not trying to commit tax fraud!
2) call the IRS with questions! It can take a while to get through the queue, but they are SUPER knowledgeable and helpful!! I have called in the past and they’ve been SO HELPFUL, and SO KNOWLEDGEABLE, and FIXED STUPID MISTAKES I MADE.
3) IF YOUR ADJUSTED GROSS INCOME IS UNDER 79K, YOU CAN USE FREE FILE, WHICH IS NEW THIS YEAR!!
Don’t fear the IRS. The wealthy do, and they want you to fear the IRS too, so you’ll vote for Republicans who want to strip the IRS of funding so they can’t audit rich people.