Standard vs Itemized Deduction

How it works

1. 1. Determine standard deduction amount

   The base standard deduction varies by filing status and is indexed annually for inflation. 2025 base amounts: $30,000 (MFJ), $22,500 (HoH), $15,000 (Single/MFS). An additional deduction is added for each qualifying person age 65 or older. Age 65+ additional amounts by year: • 2024: $1,950 per person (Single/HOH); $1,550 per person (MFJ/MFS) • 2025: $2,000 per person (Single/HOH); $1,600 per person (MFJ/MFS) For MFJ filers, both spouses are evaluated independently — if both are 65+, the additional amount is doubled. For all other filing statuses, only the primary client's age is counted. If a client's age is unknown, no additional deduction is applied. MFS filers use the same per-person amount as MFJ (not the Single amount).

   Standard Deduction = Base Amount + (Age 65+ Adjustment × qualifying persons)
   MFJ maximum (both spouses 65+): Base + 2 × per-person amount
   Single/HOH: Base + per-person amount (primary client only)

2. 2. Calculate total itemized deductions

   Sum all Schedule A deductions: state/local taxes (SALT, year-based cap), mortgage interest (first $750k debt), charitable contributions, medical expenses (>7.5% AGI), and other qualifying deductions.

   Total Itemized = min(SALT, SALT Cap) + Mortgage Interest + Charitable + max(0, Medical - AGI × 0.075) + Other
   SALT Cap: $10,000 (2024), $40,000 (2025), $40,400 (2026) for MFJ/Single/HOH; half for MFS

3. 3. Compare standard vs itemized

   Select the larger of standard deduction or total itemized deductions. This becomes the baseline deduction amount before any top-bracket haircut adjustment.

   Deduction Amount = max(Standard Deduction, Total Itemized)

4. 4. Apply top-bracket limitation (tax years 2026 and later, itemizers only)

   For tax years 2026 and later, taxpayers who itemize and have any taxable income in the 37% top bracket face the OBBBA Section 70101 haircut (IRC Section 68 restored). The otherwise-allowable itemized deductions are reduced by 2/37ths of the lesser of (a) total itemized deductions or (b) taxable income in the 37% bracket. This is a one-pass calculation — it measures against pre-haircut taxable income (Form 1040 line 15, including both ordinary income and capital gains above the bracket threshold). No iterative convergence is needed because AGI is fixed before itemized deductions are taken. The QBI deduction (Section 199A) is not subject to this haircut — it operates independently of Section 68 and is not recomputed after the haircut. Standard-deduction filers are completely unaffected. No carryforward is created for the disallowed amount. Practical effect: each dollar of itemized deduction that reduces 37%-bracket income is worth 35 cents in tax savings (37% rate with the 2/37ths haircut applied) instead of the full 37 cents. For clients below the 37% bracket threshold, the haircut is zero. 2026 bracket thresholds (inflation-indexed each year): MFJ: $768,700 Single/MFS: $640,600

   Exposure = max(0, Pre-Haircut Taxable Income - 37% Bracket Floor)
   Haircut Amount = (2/37) x min(Total Itemized Deductions, Exposure)
   Net Allowable Itemized = Total Itemized Deductions - Haircut Amount

5. 5. Calculate tax benefit

   The incremental tax savings from itemizing (if applicable) equals the excess itemized amount (net of any top-bracket haircut) times the marginal tax rate. For clients in the 37% bracket in 2026+, the effective marginal value of itemized deductions is 35% rather than 37%.

   Itemizing Benefit = max(0, Net Allowable Itemized - Standard Deduction) × Marginal Rate
   (For 37%-bracket itemizers in 2026+: effective marginal value per dollar = 35%, not 37%)

Worked example

**Step 1: Standard Deduction**
- MFJ base standard deduction (2024): $29,200
- No age 65+ adjustment (neither spouse is 65+)
- Standard Deduction = $29,200

**Step 2: Total Itemized Deductions**
- SALT (state tax + property tax): $12,000 + $8,000 = $20,000
  → Capped at $10,000
- Mortgage interest: $15,000 (within $750k debt limit)
- Charitable contributions: $8,000
- Medical expenses: $10,000
  → AGI threshold: $180,000 × 7.5% = $13,500
  → Deductible amount: max($10,000 - $13,500, $0) = $0
- Total Itemized = $10,000 + $15,000 + $8,000 + $0 = $33,000

**Step 3: Compare**
- Standard: $29,200
- Itemized: $33,000
- **Recommendation: Itemize** (saves additional $3,800)

**Step 4: Top-bracket limitation**
- Taxable income = AGI $180,000 - itemized $33,000 = $147,000
- MFJ 37% bracket threshold (2024): N/A (haircut starts in 2026)
- Haircut amount = $0 (year 2024; provision not yet effective)

**Step 5: Tax Benefit**
- Excess itemized: $33,000 - $29,200 = $3,800
- Marginal rate: 24%
- Additional tax savings: $3,800 × 0.24 = $912
      

Real-world context

What drives the result

Assumptions

• Standard deduction amounts are $30,000 (MFJ), $22,500 (HoH), $15,000 (Single) for 2025
• SALT deduction cap: $10,000 for 2024, $40,000 for 2025, $40,400 for 2026 (MFJ/Single/HOH), half for MFS — set by the One Big Beautiful Bill Act, which raises the cap 1% a year through 2029 and returns it to $10,000 in 2030. For households above the OBBBA MAGI threshold ($500,000 in 2025, $505,000 in 2026) the cap is reduced by 30% of the excess, floored at $10,000, before it enters the itemized total; the Section 68 top-bracket haircut is then applied to that already-reduced total. See the SALT Deduction page.
• Mortgage interest deduction limited to $750,000 of acquisition debt for post-2017 loans
• Medical expense threshold is 7.5% of AGI (permanent after TCJA)
• Taxpayer keeps adequate records to substantiate itemized deductions
• Charitable contributions do not exceed 60% of AGI (cash) or 30% of AGI (appreciated property)
• OBBBA Section 70101 top-bracket haircut (IRC Section 68) applies to all itemizers with income in the 37% bracket for tax years 2026 and later; QBI (Section 199A) is not subject to this haircut; no carryforward is generated for disallowed amounts

Limitations

• The pre-TCJA Pease limitation (3% phaseout with 80% floor, IRC Section 68 pre-2018) is not modeled for years it applied; the restored Section 68 haircut under OBBBA Section 70101 is fully modeled for 2026+
• Assumes taxpayer qualifies for standard deduction (some dependents may not)
• Does not include all possible itemized deductions (e.g., casualty losses, gambling losses)
• State tax treatment may differ significantly from federal (some states do not allow standard deduction)
• Blindness adds an additional standard deduction equal to the age 65+ amount; this is not modeled

Related

• Deduction Bunching Strategy — Bunching strategy concentrates deductions to exceed standard deduction in alternating years
• Mortgage Interest Deduction — Mortgage interest only provides tax benefit when itemizing exceeds standard deduction
• SALT Deduction (State and Local Taxes) — SALT cap significantly reduced number of taxpayers who itemize
• Charitable Contributions Deduction — Charitable gifts only reduce taxes if total itemized deductions exceed standard deduction