Hal_Al:
After further searching, I get the same result by a different calculation. The maximum IRA contribution is equal to net earnings, defined as profit x 0.9235, in my case 9026 x 0.9235 = 8336.
Apparently the difference between profit and net earnings is Social Security and Medical payment.
SE tax is net earnings x 0.153 = 8336 x 0.153 = 1275, which is what TT comes up with. Half of that amount becomes a deduction on the personal tax calculation.
