Which specific lines and forms on the 2025 Form 1040 and associated schedules will show the senior deduction and MAGI add‑backs?

1. The starting point: AGI is on Form 1040, Line 11

All guidance and practitioners’ writeups point to the AGI on Form 1040 (Line 11) as the base number used to calculate MAGI for the 2025 senior deduction; taxpayers begin with the Line 11 AGI and then apply the statutory “add‑backs” to reach MAGI used in the phase‑out tests ^{[1] [5]}.

2. Where the MAGI add‑backs live: Schedule 1‑A, Part I (new worksheet)

Several preparer guides and community experts report that the IRS introduced Schedule 1‑A (a supplemental worksheet) for 2025 and that Part I of Schedule 1‑A is where taxpayers add back the specific excluded items — notably foreign earned income exclusion, housing exclusion, and certain U.S. territory exclusions — to AGI to compute MAGI for the senior deduction ^{[2] [3] [6]}.

3. What to add back to AGI to make MAGI (the common items)

The most consistently cited add‑backs are the foreign earned income and housing exclusions and amounts excluded because they come from U.S. territories (Puerto Rico, Guam, American Samoa, Northern Mariana Islands); these items are added to Line 11 AGI on Schedule 1‑A to produce MAGI for the senior deduction test ^{[1] [3] [6]}. Multiple sources note that for most seniors MAGI equals AGI because few taxpayers have these specific exclusions ^{[7] [8]}.

4. What is not an automatic add‑back: nontaxable Social Security

Practitioner threads and preparer FAQs explicitly flag that nontaxable Social Security benefits are generally not added back when calculating MAGI for the 2025 senior deduction; only the taxable portion that flows into AGI affects the starting AGI number ^[9]. That distinction matters because many retirees assume all Social Security must be reconcilable into MAGI — the reporting shows that it does not unless already included in AGI ^[9].

5. Where the senior deduction itself is calculated: Schedule 1‑A, Part V

Guides and community solutions state that the actual senior deduction computation — entering the base $6,000 (single) or $12,000 (MFJ), applying the 6‑cent per dollar phase‑down, and computing the taxpayer’s allowed amount — is performed on Schedule 1‑A (Part V labeled “Enhanced Deduction for Seniors” in the treatments) and that the schedule’s result is the figure to transfer to Form 1040/1040‑SR Line 13b (Schedule 1‑A Part V → Line 13b) ^{[2] [3] [4]}.

6. Where the deduction appears on the Form 1040 / 1040‑SR

Multiple tax coverage sources say the final senior deduction amount will appear as a separate entry on the Form 1040 or 1040‑SR — commonly noted as Line 13b in preparer guides — and that Form 1040‑SR uses identical numbering and calculations to Form 1040, merely formatted for seniors ^{[4] [8] [10]}. Some secondary sources reference “Line 13” or the general “additional deduction” slot, but the consensus across preparer guidance and user threads places the Schedule 1‑A output on Line 13b ^{[8] [3]}.

7. Practical notes and remaining ambiguities

Reporting consistently emphasizes that for most seniors MAGI will equal AGI (Line 11) and that only taxpayers with foreign exclusions or territory income need Schedule 1‑A add‑backs; practitioners also warn to avoid conflating the permanent additional standard deduction for age/blindness with this temporary $6,000/$12,000 senior bonus, which is separately computed and reported ^{[7] [10] [11]}. The public sources used here are preparer guides, IRS MAGI explanations, and tax‑help sites; if the IRS publishes official Form 1040 and Schedule 1‑A instructions with different line numbers or labels, that authoritative form instruction would control — the available sources consistently point to Line 11 (AGI), Schedule 1‑A Part I for MAGI add‑backs, Schedule 1‑A Part V for the deduction math, and transfer of the final result to Form 1040/1040‑SR Line 13b ^{[1] [2] [3] [4]}.