Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Higher-value path
Invest
Investing path value
$380,411
Mortgage interest saved
$95,593
Difference
$284,818
Months shaved off mortgage
97
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter current mortgage balance ($).
- 2Enter mortgage rate (%).
- 3Enter years remaining.
- 4Enter extra monthly amount ($).
- 5Enter expected investment return (%).
- 6Read your higher-value path on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
This calculator focuses specifically on making extra principal payments on an existing mortgage versus redirecting that same monthly amount into a taxable brokerage account. It models the interest saved and years shaved off the loan from extra payments against the compounded growth of investing instead, using your mortgage rate and expected market return.
Worked example
Using the values the calculator loads with:
Inputs
- Current mortgage balance: 280000 $
- Mortgage rate: 6 %
- Years remaining: 25
- Extra monthly amount: 400 $
- Expected investment return: 8 %
Results
- Higher-value path: Invest
- Investing path value: $380,411
- Mortgage interest saved: $95,593
- Difference: $284,818
- Months shaved off mortgage: 97
What each field means
Inputs
- Current mortgage balance ($)
- The current mortgage balance used in the calculation, measured in $. Starts at 280000 $ so you have a working example on load.
- Mortgage rate (%)
- The mortgage rate used in the calculation, measured in %. Starts at 6 % so you have a working example on load. Accepted range: 0–15 %.
- Years remaining
- The years remaining used in the calculation. Starts at 25 so you have a working example on load. Accepted range: 1–30.
- Extra monthly amount ($)
- The extra monthly amount used in the calculation, measured in $. Starts at 400 $ so you have a working example on load.
- Expected investment return (%)
- The expected investment return used in the calculation, measured in %. Starts at 8 % so you have a working example on load. Accepted range: 0–20 %.
Results
- Higher-value path
- Returned as a plain value and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Investing path value
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Mortgage interest saved
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Difference
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Months shaved off mortgage
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How is this different from the general payoff-vs-invest tool?
This one is mortgage-specific and models exact amortization with your extra payment reducing principal each month, showing precisely how many months it shortens the loan by.
Which option is more predictable?
Paying extra principal is fully predictable — you know your mortgage rate. Investing depends on market performance, which can vary widely and even be negative over shorter windows.
Does prepaying trigger any penalty?
Check your loan terms — most conventional mortgages issued in the last decade don't have prepayment penalties, but some older or non-conforming loans do.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Extra Mortgage Payment vs Invest the Difference Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/extra-mortgage-payment-vs-invest-difference
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/extra-mortgage-payment-vs-invest-difference" target="_blank" rel="noopener">Extra Mortgage Payment vs Invest the Difference Calculator — RevenueLab</a> (2026).</p>
Source: [Extra Mortgage Payment vs Invest the Difference Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/extra-mortgage-payment-vs-invest-difference) (2026).