I am using Free Fillable Forms on Irs.gov. I have a 1099-misc form with amount in box 3. This is from my bank for ATM fees they reimbursed me. I also have several W2-G's gambling winnings. You cannot add a 1099-Misc in the forms section of the program but can add the W2-G's. All of this income belongs on Line 21 of form 1040. On the program I list Gambling Winnings ATM fee reimbursement in the gray area on Form 1040 and the amount in the gray area to the right. The program than "Does the Math" and puts the total on Line 21 of the Form 1040. You cannot manually enter a number onto line 21 of the tax form. I am getting an efile reject stating W2G gambling winnings reported in Forms section are not equal to or less than amount on line 21. Sent error code to IRS and they were no help.
Be warned, this answer isn't pretty, and completely defeats your efforts to e-"phile". But it will be timely.
Time is of the essence... or it's not
If you owe any money, you need to pay up by April 17. Period. This is separate from filing your taxes. Obviously it's expedient to do both together.
If the IRS owes you money (or if you're even), there is no penalty for filing your taxes late. So if IRS owes you a refund, the time pressure is off.
If you owe money, then you have two simple choices: File a "request for extension of time to file" Form 4868, which gives you a way to pay, and pay more than you will finally owe. OR, "do what it takes" to get this online system to take your numbers and accept your money.
... and then, fix it later
At your leisure, you can amend your taxes at any time up to 3 years later. You do this by filing Form 1040X. The secret to success in 1040X is to (as a scratchpad) fill out two full, paper 1040 forms.
- the way you actually did file your taxes - in your case this would be the numbers that the system was able to accept.
- the way you want your taxes to be. (i.e. that include all the deductions you want to take).
In the 1040X you summarize the differences by lifting numbers from each form as instructed. You explain changes and attach any new schedules.
Doing a 1040X is a chore, but there's money at the end of the rainbow, so I have always found it worth doing.
There's no need to attach or add the 1099-MISC to the online form, just like you wouldn't need to attach it for a paper filing.
Since Free File Fillable Forms doesn't do anything beyond basic math, you need to calculate the total for Line 21 Other Income yourself. If you have multiple sources of income that go on that line, you just need to add them yourself and put the total on that line.
Putting the total on that line is a bit confusing in their interface, though. There are three boxes on the line. The first is for a description of the Other Income you're including. The second is for the dollar amount of the total. And the third box isn't editable directly; the software just copies the value from the second box to the third box when it does its calculations. Seems pretty weird, yes, but that total you calculate of all your Other income just needs to do in that middle box to be able to file.