After-tax mortgage rate vs after-tax investment return is the right comparison. MID matters only if you itemise; LTCG and account type matter on the invest side.
$47,327 + invest
Invest wins on paper. The after-tax investment return exceeds the after-tax mortgage rate. Risk-adjusted, factor in your tolerance for market volatility, the mortgage rate is guaranteed, the investment return is not.
MID benefit assumed only if your mortgage interest + other itemised deductions exceed the standard deduction. For most post-2018 households the standard deduction wins, so set MID off. Taxable LTCG modelled at 15% federal + state; Traditional IRA at marginal; Roth tax-free.
Worth runs the after-tax math with your actual mortgage rate, marginal bracket, and account type. Join the waitlist.
When your total itemised deductions (mortgage interest + SALT capped at $10k + charitable) exceed the standard deduction ($29,200 MFJ / $14,600 single in 2025). For most middle-income post-2018 households, the standard deduction wins and MID provides no marginal benefit.
Because the after-tax return is what matters. A Roth grows tax-free (return × 1). A taxable brokerage loses 15% LTCG + state on appreciation. A Traditional IRA gets taxed at marginal on withdrawal, so the effective return is r × (1 − marginal).
The mortgage rate is guaranteed; the investment return is expected. Even when invest wins on paper, the certainty of the mortgage rate has value, call it a 1-2pt risk premium against the headline gap before deciding.