Which sheet does it land on?
A rule you understand is only half an answer. The other half is the schedule it goes on — and where a deduction sits decides which taxes it reduces, not just how much.
The business
Where profit is worked out, and the tax charged on it.
Schedule C
Profit or Loss from Business (Sole Proprietorship)
Who files itEveryone self-employed without a separate entity
Schedule SE
Self-Employment Tax
Who files itAnyone with $400 or more of net earnings from self-employment
Schedule F
Profit or Loss From Farming
Who files itFarmers and ranchers
Schedule J
Income Averaging for Individuals With Income From Farming or Fishing
Who files itFarmers and commercial fishermen, and nobody else
Other income
Rent, royalties and the sale of assets, generally outside self-employment tax.
Deductions
Adjustments to income, the new deductions, and itemizing.
Schedule 1
Additional Income and Adjustments to Income
Who files itAnyone with income or adjustments that Form 1040 has no line for
Schedule 1-A
Additional Deductions
Who files itWorkers claiming the tips, overtime, car loan interest or senior deductions
Schedule A
Itemized Deductions
Who files itFilers whose itemised deductions beat the standard deduction
