According to What Is Modified Adjusted Gross Income? in the IT 1040/SD 100 Instructions:
Modified adjusted gross income (MAGI) is your Ohio adjusted gross income (Ohio IT 1040, line 3) plus your business income deduction (Ohio Schedule of Adjustments, line 12). If you did not take a business income deduction, your MAGI matches your Ohio adjusted gross income.
So, this would equal
- Form IT 1040 line 1: Federal adjusted gross income from federal Form 1040 or 1040-SR, line 11, plus
- Form IT 1040 line 2a: Additions from Ohio Schedule of Adjustments line 11, minus
- Form IT 1040 line 2b: Deductions from Ohio Schedule of Adjustments line 44, plus
- Schedule of Adjustments, line 12: Business income deduction from Schedule of Business Income, line 13.
You can find Form IT 1040, SD 100 and their instructions at Tax Forms.