Line 4d can be smaller because of your answers to the questions about your 1099R. Did you move some of the 1099R distribution to another account? Did you do a Rollover? It would say Rollover by line 4. Or you said you had a basis in the 401k. Go back and check your 1099R entries.
Line 5 is for Social Security. It changes depending on your other income
Up to 85% of Social Security becomes taxable when all your other income plus 1/2 your social security, reaches:
Married Filing Jointly: $32,000
Single or head of household: $25,000
Married Filing Separately: 0
