Calculate

Line 1a = Sum of W-2 Box 1 from all W-2s
Line 1z = Line 1a  (only W-2 income for this profile)
Line 9  = Line 1z  (total income = wages only)

STEP 2: ADJUSTMENTS TO INCOME (Schedule 1)

Only student loan interest applies for this profile:

IF student_loan_interest > 0:
    raw = min(student_loan_interest, 2500)
    MAGI = Line 9  (total income, before adjustments)

    IF MAGI <= 85000:
        deduction = raw
    ELIF MAGI >= 100000:
        deduction = 0
    ELSE:
        deduction = raw * (1 - (MAGI - 85000) / 15000)
        deduction = round(deduction, 2)

    Schedule_1_Line_21 = deduction
    Schedule_1_Line_26 = deduction
    Line_10 = deduction
ELSE:
    Line_10 = 0

STEP 3: ADJUSTED GROSS INCOME

Line 11 = Line 9 - Line 10

This is the AGI -- the most important number on the return. It determines eligibility for credits and deduction phaseouts.

STEP 4: SCHEDULE 1-A DEDUCTIONS (New for 2025)

Calculate each applicable deduction with MAGI phaseout:

MAGI_for_1A = Line 11  (AGI)

# Phaseout function (shared by all Schedule 1-A deductions)
def apply_phaseout(amount, magi):
    if magi <= 75000: return amount
    if magi >= 100000: return 0
    return round(amount * (1 - (magi - 75000) / 25000), 2)

# Tip deduction (Line 1)
tip_deduction = apply_phaseout(tip_income, MAGI_for_1A)

# Overtime deduction (Line 2)
overtime_deduction = apply_phaseout(overtime_pay, MAGI_for_1A)

# Auto loan interest (Line 3) -- max $10,000
auto_loan_deduction = apply_phaseout(min(auto_loan_interest, 10000), MAGI_for_1A)

# Senior deduction (Line 4) -- only if age 65+
IF age >= 65:
    senior_1a_deduction = apply_phaseout(4000, MAGI_for_1A)
ELSE:
    senior_1a_deduction = 0

Schedule_1A_Line_5 = tip_deduction + overtime_deduction + auto_loan_deduction + senior_1a_deduction
Line_12c = Schedule_1A_Line_5

STEP 5: STANDARD DEDUCTION

IF age >= 65:
    Line_12a = 17750  (single, 65+: $15,750 + $2,000 additional)
ELSE:
    Line_12a = 15750  (single, under 65)

STEP 6: TOTAL DEDUCTIONS

Line_12b = 0  (no charitable deduction for this profile)
Line_13 = 0   (no QBI deduction for W-2 filers)
Line_14 = Line_12a + Line_12b + Line_12c + Line_13

STEP 7: TAXABLE INCOME

Line_15 = max(Line_11 - Line_14, 0)

STEP 8: TAX FROM BRACKETS

Apply 2025 single filer brackets:

taxable = Line_15

if taxable <= 11925:
    tax = taxable * 0.10
elif taxable <= 48475:
    tax = 1192.50 + (taxable - 11925) * 0.12
elif taxable <= 103350:
    tax = 5578.50 + (taxable - 48475) * 0.22
elif taxable <= 197300:
    tax = 17651.00 + (taxable - 103350) * 0.24
elif taxable <= 250525:
    tax = 40099.00 + (taxable - 197300) * 0.32
elif taxable <= 626350:
    tax = 57131.00 + (taxable - 250525) * 0.35