About the Pay Off Debt or Invest Calculator
This pay off debt or invest calculator answers a classic question: if you have extra money each month, should it go toward your debt or into investments? It simulates both strategies month by month using the same total budget — your minimum payment plus the extra — so the comparison is fair.
In the “pay off first” strategy, all of the budget goes to the debt until it is gone, then the whole amount is invested. In the “invest” strategy, you pay only the minimum and invest the extra, adding the freed-up minimum payment once the debt is paid off. At the end of your time horizon the tool compares net worth (investments minus any remaining debt).
The rule of thumb is simple: paying off debt is a guaranteed return equal to its interest rate, while investing offers an expected but uncertain return. The calculator ignores taxes, employer 401(k) matches and market volatility, so treat close results as a tie and lean toward the guaranteed return of paying debt when rates are high.
How to use the pay off debt or invest calculator
- 1Enter your debt balance, its interest rate and the minimum monthly payment.
- 2Enter how much extra cash you have each month.
- 3Set a realistic expected investment return and your time horizon.
- 4Compare net worth under both strategies and check the chart.
- 5If results are close, favour paying off debt — it is a guaranteed return.
Formula and method
Both strategies spend the same monthly budget (minimum payment + extra). Each month the debt balance grows by one month of interest and then the payment is subtracted; whatever is left of the budget is invested and grows at the expected return, compounded monthly. In the pay-off-first strategy the payment is the whole budget until the debt is gone; in the invest strategy it is only the minimum.
Net worth at the horizon is the investment balance minus any debt left. Because paying off debt earns exactly its interest rate risk-free, the invest strategy only wins when the expected return is higher than the debt rate — and the calculator does not adjust for taxes, fees or the risk of lower returns.
- B
- Debt balance
- I
- Investment balance
- APR
- Debt interest rate
- R
- Expected annual investment return
- budget
- Minimum payment + extra cash each month
Worked examples
7% car loan vs 8% expected return
Putting $800 a month at the $15,000 loan clears it in 20 months, then everything is invested — about $113,344 after 10 years. Paying the $300 minimum (debt-free in 60 months) and investing $500 ends at about $113,834. Investing wins by only $490, a near-tie that assumes a steady 8% return.
22% credit card debt
At 22% the card is far more expensive than the 8% investments earn. Paying $760 a month kills the debt in 19 months and leaves about $109,307 after 10 years, versus $104,030 investing the extra — paying off first comes out $5,277 ahead.
4% student loan over 15 years
With a low 4% loan and a 10% expected return, investing the $300 extra from day one grows to about $177,288 of net worth after 15 years, versus $168,743 if the loan is paid off first in 42 months — about $8,545 more, in exchange for market risk.
Frequently asked questions
Should I pay off debt or invest?+
Compare the debt’s interest rate with the after-tax return you realistically expect. High-interest debt such as credit cards (15%+) should almost always be paid first. For low-rate debt under about 4%–5%, investing often wins over long horizons, especially inside tax-advantaged accounts.
Should I still get my 401(k) match while paying off debt?+
Usually yes. An employer match is an instant 50%–100% return on the matched contributions, which beats paying down almost any debt. Contribute enough to get the full match, then direct extra cash by comparing rates.
Is paying off debt a guaranteed return?+
Yes. Every dollar of principal you repay early saves interest at the loan’s rate with no market risk. A 7% loan paid off early is equivalent to a risk-free 7% return, which is hard to find in safe investments.
Should I pay off my mortgage or invest?+
Mortgages usually have lower rates and may be tax-deductible, so investing often comes out ahead over decades. Many people still value being debt-free before retirement. Model it here with your mortgage rate, payment and horizon.
What return should I assume for investing?+
Broad US stock market indexes have historically averaged roughly 10% a year before inflation (about 7% after inflation) over long periods, but returns vary widely from year to year. A conservative 6%–7% is a reasonable planning assumption for a diversified portfolio.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.