Overpay Mortgage vs Invest Comparator
Compare paying off your mortgage early against investing extra cash in index funds. Calculate net wealth, interest saved, and breakeven return rates.
Mortgage & Investment Assumptions
Strategy A: Overpay Mortgage
- Debt-Free: Paid off in 14.9 years instead of 20.
- Guaranteed Return: 5.50% risk-free return on your money.
- Ending Liquid Portfolio: $179,942.58 (reinvesting after payoff).
- Best For: Risk-averse homeowners seeking peace of mind and lower monthly overhead.
Strategy B: Invest in Index Funds
- Mortgage Term: Remains full 20 years on schedule.
- Compounding Horizon: Extra $400 compounds for 240 full months.
- Ending Liquid Portfolio: $204,535.93.
- Best For: Wealth maximizers willing to accept market volatility for greater net worth.
About this tool
How to use it
- Input your current mortgage balance, remaining loan term in years, and fixed mortgage interest rate (APR).
- Specify the surplus cash you have available each month to allocate towards debt paydown or market investing.
- Enter your expected stock market return (e.g. 7% to 10% for global equity index funds) and capital gains tax drag percentage.
- Click 'Compare Wealth Outcomes' to evaluate total liquid wealth, interest saved, and the breakeven market return rate.
Why it matters
Homeowners often struggle with the emotional desire to be mortgage-free versus the financial opportunity cost of compounding market returns. Quantifying the exact dollar differential between early debt payoff and index investing empowers individuals to balance risk, liquidity, and long-term net worth.
When to use it
Use this comparator when refinancing a home loan, receiving an annual salary bonus, setting monthly budget allocations, or deciding what to do with extra cash after maxing out employer retirement contributions.
Good to know
Calculations compare both strategies across the exact same total time horizon. When overpaying, once the loan reaches a zero balance, the full monthly payment is automatically reinvested into the market for the remainder of the original term. Tax drag assumes standard taxable brokerage accounts; use 0% for tax-advantaged accounts like Roth IRAs or UK ISAs.
Common questions
Is paying off a mortgage early considered a guaranteed return?
Yes. Every dollar paid toward your mortgage principal eliminates interest compounding at your exact loan interest rate. For example, overpaying a 6.0% mortgage yields a guaranteed, risk-free return of 6.0%, which is not subject to stock market volatility or downside drawdowns.
What is the breakeven investment return rate?
The breakeven rate is the minimum gross annual investment return required in the stock market to outperform paying off your mortgage, after adjusting for capital gains taxes. If your mortgage rate is 6% and your capital gains tax rate is 15%, your market investments must generate over 7.06% just to match debt paydown.
What about liquidity and emergency access to cash?
Liquidity is a crucial non-mathematical factor. Money invested in brokerage accounts can be liquidated within days in the event of an emergency. Money paid into your home equity is trapped and can only be accessed by selling the property or taking out a home equity loan (HELOC), which may not be approved during sudden job loss.
What is the hybrid 50/50 approach?
Many financial planners recommend a split strategy: allocating 50% of monthly surplus cash toward mortgage overpayments and 50% into low-cost index funds. This builds accessible liquid investments while simultaneously reducing fixed monthly living expenses.
Does this tool factor in mortgage interest tax deductions?
In the United States, homeowners who itemize deductions can deduct mortgage interest. However, under standard deduction thresholds, the majority of households do not itemize. If you itemize, your effective mortgage interest rate is slightly lower than your nominal APR.