For 1099 contractors & freelancers
Yes, contributions to a self-employed retirement plan are deductible, as an adjustment to income rather than on Schedule C.
Schedule 1 (Form 1040), line 16. Not Schedule C.
For a SEP IRA, a self-employed person can contribute roughly 20% of net self-employment earnings (after the deduction for half of self-employment tax), up to $72,000 for 2026.
A solo 401(k) adds an employee deferral on top of that, which allows larger contributions at lower income levels.
SEP contributions can usually be made up until your tax filing deadline, including extensions, and still count for the prior year.
Contribution confirmations from your plan provider.
Sources
General information, not tax advice. For your specific situation, check with a CPA or Enrolled Agent.