Investment returnHigh modeled impact
Higher input raises the modeled result
Return changes the compounded value of monthly investing under both paths.
Mortgage · Equal-cash-flow comparison
Mortgage vs Invest Calculator
Compare paying a mortgage faster with investing the same extra monthly cash—using equal household cash flow through the original mortgage payoff date.
Same monthly budget Deterministic month-by-month math Educational scenario
Your result
Modeled advantage under these assumptions
Invest First ahead by
$36,604
At the original mortgage payoff date, Invest First has the larger modeled investment balance. Both mortgages are fully paid and home equity is the same.
Same monthly household cash flow $2,480 per month
Regular mortgage payment$1,980
Original payoff horizon20 years
Mortgage First payoff14 years 1 month
Time saved5 years 11 months
Regular-schedule interest$175,168
Mortgage First interest$118,261
Interest saved$56,907
Break-even investment return5.12%
Mortgage First investments$217,165
Invest First investments$253,768
The 7.00% investment-return assumption is above the modeled 5.12% break-even return. Invest First finishes about $36,604 ahead.
Mortgage balance comparison
Regular vs. accelerated payoff
Mortgage First directs the extra cash to principal until payoff. Invest First follows the regular schedule.
Regular schedule Mortgage First
Regular payoff20 years
Mortgage First payoff14 years 1 month
Modeled interest saved$56,907
Investment balance comparison
Mortgage First vs. Invest First
Both strategies use the same monthly budget; only the timing of mortgage and investment cash flows changes.
Mortgage First Invest First
Mortgage First investments$217,165
Invest First investments$253,768
Ending difference$36,604
Return sensitivity
Five investment-return scenarios
Mortgage terms and extra cash stay unchanged. Each return is a scenario—not a prediction or recommendation.
2%
Mortgage First$40,471
4%
Mortgage First$16,987
6%
Invest First$15,816
8%
Invest First$60,891
10%
Invest First$122,071
At 2% and 4%, Mortgage First leads; at 6%, 8%, and 10%, Invest First leads in the default scenario.
Through the Lens
What drives this result?
Controlled, deterministic sensitivity around your current inputs reveals which assumptions move the strategy ending-wealth difference most.
Remaining termHigh modeled impact
Higher input raises the modeled result
Time changes both mortgage interest and investment compounding.
Mortgage rateHigh modeled impact
Higher input lowers the modeled result
The rate changes scheduled interest and the value of paying principal sooner.
Extra monthly cashHigh modeled impact
Higher input raises the modeled result
This is the equal monthly amount directed to mortgage principal or investing.
High modeled impact means an input changes this output substantially around the current scenario. Rankings compare controlled 10% input changes; they do not measure risk, probability, personal importance, controllability, suitability, advice, or forecasts. A driver can also change which strategy leads; labels do not measure risk tolerance or certainty.
Meaning
What this means
The comparison holds household cash flow constant.
In this scenario, Invest First finishes with a modeled advantage of $36,604 at the original 20 years payoff date.
Mortgage First pays the loan off in 14 years 1 month, saves about $56,907 of interest, then invests the entire freed monthly budget. Invest First keeps the regular mortgage and invests the extra cash every month.
Implication
The modeled break-even annual investment return is 5.12%. Returns above or below that point can change which strategy finishes ahead.
That numerical break-even is not a decision rule. Paying mortgage principal creates a contractual interest saving; an investment return is uncertain and can arrive unevenly or be negative.
Fair comparison
Why the cash flows are comparable
Mortgage First
The regular payment plus all extra cash goes to the mortgage. In the payoff month, any unused part of that budget is invested immediately. From the following month to the original horizon, the full monthly budget is invested.
Invest First
The regular mortgage payment follows its original schedule while the extra cash is invested at each month-end. Any unused cents in the final scheduled mortgage payment are also invested.
Home equity is intentionally excluded from the final difference.
Both strategies have a fully paid mortgage at the same comparison date and therefore the same modeled home equity. The ending investment balance difference is the modeled position difference.
Methodology
How the calculator works
Monthly mortgage rate
annual mortgage rate ÷ 12Regular mortgage payment
P × r × (1 + r)^n ÷ ((1 + r)^n − 1)When r = 0: P ÷ nExact monthly investment rate
(1 + annual investment return)^(1 ÷ 12) − 1Month-end investment update
prior balance × (1 + monthly investment rate) + contributionSame household cash flow
regular mortgage payment + extra monthly cashEnding wealth difference
Invest First ending investments − Mortgage First ending investmentsBreak-even return
bisection search for an ending wealth difference of approximately $0The engine simulates every month through the original payoff horizon. Payments never exceed the amount due; unused payoff-month cash is redirected to investing so each strategy uses the same household budget.
Risk, liquidity, and taxes
The higher modeled ending value is not automatically the better choice
Risk is different
- Mortgage interest avoided is based on the entered loan rate and modeled payments.
- Investment returns are uncertain, volatile, and not earned in a smooth line.
- Sequence, behavior, and the ability to stay invested can change real outcomes.
Liquidity and taxes matter
- Money invested may be more accessible than home equity, depending on account and market conditions.
- Mortgage prepayments can be restricted or penalized by a lender.
- Investment account taxes, deductions, contribution limits, and tax shelters can materially change the comparison.
Guardrails
Assumptions and limitations
This educational scenario assumes:
- A fixed mortgage rate for the full remaining amortization, with monthly payments and interest calculated as annual rate ÷ 12
- No refinancing, renewal-rate changes, prepayment penalties or limits, lender restrictions, or payment-frequency changes
- A constant annualized investment return converted to an exact monthly rate, with no volatility or sequence variation
- Investment contributions occur at month-end, with no withdrawals
- Extra monthly cash remains available through the comparison horizon
Actual returns, mortgage terms, and personal circumstances vary.
Actual lender calculations can differ by contract, jurisdiction, compounding convention, payment frequency, rate changes, and mortgage terms. Taxes, investment fees, trading costs, insurance, home appreciation, inflation, emergency reserves, and transaction costs are excluded.
The entered investment return may be treated as after-tax and after-fee if you adjust it yourself. Results are scenarios—not forecasts or financial advice.
Known-answer checks
Examples used to validate the engine
Standard payment$300,000 at 5% over 20 years produces a regular monthly payment of $1,979.87.
Default scenario$500 extra pays the mortgage in month 169, saves about $56,907 of interest, and produces a break-even return near 5.12%.
Equal cash flowEvery simulated month allocates the same regular payment plus extra cash under both strategies.
Edge casesZero rates, zero extra cash, zero investment returns, payoff-month remainders, large prepayments, and invalid values are tested.
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