cost-calculation
Mortgage vs. Invest Calculator (2026) — Extra Payment or Invest the Difference?
If you have an extra $500/month, should you pay down your mortgage or invest it? Mortgage payoff is a fixed, predictable reduction in interest at your effective after-tax mortgage rate. Investing has a higher expected return but isn't certain. This calculator computes both scenarios — total interest saved vs. after-tax investment growth — and gives you a verdict based on the math and the behavioral liquidity trade-off.
Educational estimate based on the inputs you entered — not financial, legal, or tax advice. Verify against your specific situation before acting on this output.
How it works
Methodology
Inputs
- Current mortgage balance
- Remaining principal on your mortgage today.
- Mortgage rate
- Annual interest rate on your mortgage.
- Months remaining
- Months left on your loan as of today.
- Extra monthly payment
- Additional amount applied to principal each month (Scenario A) or invested (Scenario B).
- Expected investment return
- Annual return assumption for the investment scenario. Historical S&P 500 real return ~7% (FRED). Past returns don't guarantee future results.
- Mortgage interest deduction tax rate
- Marginal tax rate applied to mortgage interest deduction. Default 0% for post-TCJA filers taking the standard deduction.
- Capital gains tax rate
- Long-term capital gains rate applied to investment growth on exit: 0%, 15%, or 20% for most filers.
Formula
Effective after-tax mortgage rate = mortgage_rate × (1 − deduction_tax_rate) Scenario A (extra mortgage payment): Simulate month-by-month amortization with payment = regular_payment + extra_payment Months saved = standard payoff months − accelerated payoff months Interest saved (gross) = standard total interest − accelerated total interest Interest saved (after-tax) = interest_saved_gross × (1 − deduction_rate) Scenario B (invest the difference): FV = Σ (m=1 to payoff_months) [extra_payment × (1 + r/12)^(payoff_months − m)] Capital gains tax = (FV − invested_principal) × cap_gains_rate After-tax value = FV − cap_gains_tax Verdict: invest if after-tax investment value > after-tax interest saved; otherwise pay down mortgage
Assumptions
- Investment returns are assumed constant; actual returns are volatile.
- Both scenarios are compared over the same time window (months to accelerated payoff).
- Standard deduction is assumed for most filers post-TCJA — change the deduction rate if you itemize.
- Capital gains tax is modeled as a single realization event (all gains taxed at exit); actual tax timing varies.
- No origination fees, refinance costs, or transaction costs are modeled.
- Government-backed mortgage lending stayed near record volume in fiscal year 2025 — FHA endorsed more than 876,000 loans and the VA guaranteed 528,340 loans — a reminder that most people running this comparison are financing at prevailing 2026 rates, not a 3% pandemic-era mortgage.
Worked examples
$200K mortgage at 6.5% — $500/month extra
- Mortgage balance
- $200,000
- Rate
- 6.5%
- Months remaining
- 240
- Extra payment
- $500
- Investment return
- 7%
- Deduction rate
- 0%
- Cap gains rate
- 15%
Extra payments save ~$67K in interest (guaranteed) and cut ~6 years off the loan. Investing $500/month over the same accelerated window at 7% net ~$69K after 15% cap gains tax — slight edge to investing in expected value, but mortgage paydown is certain. Close call; liquidity preference often tips the decision.
Low-rate mortgage (3.5%) vs. investing
- Mortgage balance
- $300,000
- Rate
- 3.5%
- Months remaining
- 300
- Extra payment
- $1,000
- Investment return
- 7%
- Deduction rate
- 0%
- Cap gains rate
- 15%
At a 3.5% mortgage rate vs. 7% expected investment return, the after-tax math strongly favors investing. Extra payment saves interest at a 3.5% guaranteed rate; investment compounding at 7% over the same window typically produces 2–3× the after-tax value of the interest saved.
Frequently asked
Questions readers ask
How do I calculate the effective after-tax mortgage rate? +
Effective after-tax mortgage rate = mortgage rate × (1 − deduction tax rate). For most filers post-TCJA (2018), the deduction rate is 0 — they take the standard deduction and get no marginal benefit from mortgage interest. So a 6.5% mortgage rate has a 6.5% effective after-tax cost. If you itemize deductions and are in the 22% bracket, your effective rate would be 6.5% × (1 − 0.22) = 5.07%. This is the fixed, predictable interest you avoid by paying down your mortgage, and it isn't subject to market risk.
Does it make more sense to invest or pay off the mortgage at 6.5%? +
At 6.5%, paying down a mortgage provides a fixed 6.5% after-tax reduction in interest cost (for most filers who don't itemize), and it isn't subject to market risk. Historically, broad market investments have returned ~7% real annually. So the expected-value math is close — and the mortgage paydown wins on a risk-adjusted basis because its savings are fixed while investing returns are not. However, if your effective after-tax mortgage rate is lower (e.g., you itemize in a high tax bracket) and you have a long time horizon, investing may produce a better long-run outcome. See also: <a href='/answers/pay-off-mortgage-early-vs-invest'>Pay off mortgage early vs. invest</a>.
What is the TCJA standard deduction change? +
The Tax Cuts and Jobs Act of 2017 (effective 2018) roughly doubled the standard deduction — to $27,700 for married filing jointly in 2024. As a result, fewer households benefit from itemizing deductions. If your total itemized deductions (mortgage interest + state/local taxes capped at $10K + charitable, etc.) don't exceed your standard deduction, you get zero incremental tax benefit from mortgage interest. That makes the effective after-tax mortgage rate equal to the stated rate for most filers.
Does home equity count as an investment? +
Home equity is a real asset with value, but it's fundamentally illiquid until you refinance, sell, or take a HELOC. Invested money in a brokerage account is accessible any day. This liquidity difference has real value — especially in an emergency. The calculator's behavioral note flags this: mortgage paydown locks up capital; investing keeps it accessible. That's a meaningful non-numerical factor in the decision.
What happens if I invest in a tax-advantaged account like a 401k or Roth IRA? +
The calculator models taxable account investing with a long-term capital gains rate. If the extra payment goes into a 401k or Roth IRA instead, the after-tax math changes significantly: traditional 401k contributions reduce taxable income now (deductible at your marginal rate); Roth IRA growth is tax-free. For most people with remaining 401k or Roth IRA contribution room, maxing tax-advantaged accounts before extra mortgage payments is often mathematically superior — but consult a CPA for your specific situation.
This tool is for educational purposes only and is not financial, legal, or tax advice. Final terms and eligibility depend on lender underwriting; consult a tax professional before acting on tax-tool output. ClearValue Lending is a funding platform.
https://clearvaluelending.com/tools/mortgage-vs-invest-calculator