Your total Social Security benefits are found in line 5a on your 1040. Your taxable Social Security benefits are in line 5b. So your nontaxable benefits are the difference between the two.
The same is true with the railroad retirement benefits reported on form RRB-1099.
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The 1040 or 1040SR is your tax return. Line 5a is total Social Security and line 5b is the Taxable amount. Have you filed yet?
How to preview your return before filing. If you want to see all the forms you have to pay any fees first.
Here is a screen shot of it