Get your taxes done using TurboTax

To enter a SPIFF with a 1099-MISC:

While in your return, type “1099-misc” in the Search box and then select the “Jump to” link. This will take you directly to the section where you can enter your 1099-MISC.

On the  follow-up screen,  enter SPIFF in the blank box, then on the next screen,  on the drop down list, check “This was a Manufacturer's incentive payment”

This will put it on line 21 of form 1040

Please see the screenshot below.