How do you actually compare payoff vs invest?
Run both paths forward over the same horizon and compare net worth at the end. Whichever ends higher, wins — for that set of assumptions.
Payoff path: each month, the extra dollars go toward principal. Over time, the loan shrinks faster, interest paid drops, and by the horizon you own more equity. Net worth contribution is the avoided interest plus the accelerated payoff.
Invest path: each month, the same extra dollars go into an investment account assumed to earn some rate of return. The loan keeps running on its original schedule. Net worth contribution is the accumulated investment balance minus the unchanged interest paid.
The calculator shows both endpoints and the difference. A positive difference means investing beat paying down debt; negative means debt payoff won. Small differences often mean both strategies are reasonable.
- Loan $50,000 · 8% rate · 60 months remaining
- Extra $200/month for 60 months
- Invest path @ 7% return (pre-tax): net worth ~+$1,200
- Payoff path: net worth ~+$2,400 (saves more interest than 7% earns)
- Payoff wins when loan rate > expected return
The comparison is a net-worth race over the same horizon. Small assumption changes can flip the winner.
The simple rule: is your rate higher or lower than your expected return?
Pre-tax, when loan rate > expected return, payoff wins. When loan rate < expected return, investing wins. This is the first-order rule; other factors adjust the margin.
Paying off a 7% loan gives a guaranteed 7% return on the money. Investing at an expected 7% gives a 7% return on average, but not guaranteed — markets can underperform in the exact horizon you care about.
If the loan rate is clearly above a reasonable expected return — high-rate credit cards at 20%, for example — payoff wins by a wide margin on both math and certainty. No serious comparison needed.
If the loan rate is clearly below — like a 3% mortgage — investing almost always wins in expectation because broad-market equity has historically returned 7-10% annualized. The middle zone (5-7% loans) is where individual circumstances matter most.
- 15%+ credit card -> always payoff. Math and peace of mind agree.
- 3% mortgage -> usually invest. Expected-value heavily favors markets.
- 6% mortgage vs 7% expected return -> margin is small; risk tolerance matters more
Start with the rate-vs-return comparison. Then let taxes, risk tolerance, and horizon refine the answer.
Why risk tolerance and taxes can flip the answer
Payoff is guaranteed; investing is not. And after-tax returns can narrow the investing lead considerably.
Payoff is a risk-free return. You know exactly what interest you save. Investing is a probabilistic return — over long horizons the market has returned well, but over 5-7 year windows the variance is real. For risk-averse borrowers, paying off often wins even when expected return suggests investing.
Taxes can narrow the investment path considerably. Investment gains in a taxable account are often taxed at 15-20%, which reduces the net return. A 7% gross return becomes ~5.6% after a 20% tax rate — now the comparison against a 6% loan rate flips.
The calculator lets you set an investment tax rate to make this apples-to-apples. Retirement accounts (401k, IRA) dodge current taxes and usually make investing more attractive — but only if the money stays locked up.
- 7% expected return in taxable account, 20% tax on gains
- After-tax effective return: ~5.6%
- 6% loan rate now beats after-tax return -> payoff wins
- Same 7% return in 401k: full 7% -> investing still wins
Account type changes the math. Payoff is certain; investing is a probability distribution. Weight accordingly for your own risk tolerance.
Frequently Asked Questions
What about partial payoff, partial invest?
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What about partial payoff, partial invest?
▾A mixed strategy is usually sensible. Many planners suggest paying off high-rate debt first (credit cards), keeping a decent emergency fund in cash, and directing the rest toward long-horizon investing. Ultra-low-rate mortgage debt is often worth keeping while investing.
Should I count the mortgage interest deduction?
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Should I count the mortgage interest deduction?
▾Only if you itemize. Post-TCJA (2018), most households take the standard deduction, which means mortgage interest provides no tax benefit. Check your actual filing status before adjusting the loan rate downward for deductibility.
How do I model uncertain investment returns?
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How do I model uncertain investment returns?
▾Run the calculator at multiple return assumptions — a bearish case (3-4%), a base case (6-7%), and a bullish case (9-10%). If payoff wins in the bearish case and investing wins in the bullish case, your risk tolerance decides.
Does this apply to student loans?
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Does this apply to student loans?
▾Yes, but with caveats. Student loan rates vary widely, deferral options exist during hardship, and forgiveness programs can change the math. Model the loan rate accurately and ignore any forgiveness expectation unless you are confident it will apply.
Open the full Payoff vs Invest Calculator
Compare the net worth impact of prepaying debt versus investing the same cash over your chosen horizon.
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