I found a calculation bug in TurboTax Desktop (Federal, [tax year]) regarding the MFJ optional deduction (or OBBA / QBI-related worksheet).
Issue:
TurboTax applies the 6% phase-out to the single base amount ($6,000), then multiplies the reduced result by 2 for married filing jointly.
The IRS/statute requires that the joint base ($12,000) be established first, then the 6% phase-out applied once based on joint income above $150,000.
The current sequence under-calculates the deduction. For example:
Correct: $12,000 − [(Joint Income − 150,000) × 0.06]
TurboTax: (6,000 − [(Joint Income − 150,000) × 0.06]) × 2
The base is hardcoded internally; it cannot be overridden in Forms.
Impact: The final deduction is lower than it should be. This affects the federal return for MFJ filers above the phase-out threshold.
Request: Please correct the order of operations so that the joint base is established first, then the phase-out is applied once
