Mortgage Down Payment vs Investment Opportunity Cost Calculator
See whether putting more money into a down payment—or investing it—grows your net worth faster over time.
How to Use This Down Payment vs Invest Calculator
Enter your home price, the two down payment amounts you're comparing, your mortgage rate, and your expected investment return. The calculator shows you which scenario produces higher net worth at the end of your chosen analysis period—taking into account home equity, investment growth, PMI costs, and interest savings.
The "alternative down payment" is the smaller amount you'd put down if you chose to invest the difference. The difference between your two down payment amounts is treated as the invested sum.
Why This Matters
This is one of the most debated personal finance decisions: should you put 20% down to avoid PMI and reduce interest, or put down less, keep more cash liquid, and invest the difference?
Here's a concrete example: On a $450,000 home, the difference between a 20% down payment ($90,000) and a 10% down payment ($45,000) is $45,000. If you invest that $45,000 at 7% annually for 10 years, it grows to roughly $88,500. But your larger down payment saves you about $31,000 in interest over those same 10 years and eliminates ~$18,000 in PMI. The math isn't obvious—it depends heavily on investment returns, your mortgage rate, and how long you hold the loan.
High-income earners with tax-advantaged space left (401k, IRA) and a stable income may benefit more from investing. First-time buyers who stretch to 20% might deplete emergency funds. There's no universal answer—which is exactly why this calculator exists.
How It's Calculated
Scenario A (Larger Down Payment): Lower loan balance → lower monthly payments, less interest, no PMI. Home equity = Home Value – Remaining Loan Balance.
Scenario B (Smaller Down Payment + Invest): Higher loan balance + potential PMI, but you invest the difference as a lump sum. Investment Value = Principal × (1 + after-tax return)^years.
Net Worth Comparison:
- Net Worth A = Home Equity (Scenario A) + savings from lower payments
- Net Worth B = Home Equity (Scenario B) + Investment Portfolio Value
- Opportunity Cost = |Net Worth A – Net Worth B|
After-tax return = Annual Return × (1 – Tax Rate). PMI is removed automatically once equity reaches 20%.
Tips & Common Mistakes
- Don't ignore PMI duration: PMI cancels when you hit 20% equity—typically 4–7 years on a normal schedule. Factor this in rather than assuming you pay PMI forever.
- Use realistic investment returns: The S&P 500 has averaged ~10% historically, but after inflation and taxes, 5–7% is more conservative and realistic for planning purposes.
- Consider liquidity: Home equity is illiquid. An investment portfolio gives you flexibility in emergencies. This calculator doesn't price in that optionality—it's worth considering separately.
- Match the analysis period to your plans: Planning to sell in 5 years? Use 5 years. Holding forever? Use 30. The winning scenario often changes at different horizons.
- Don't forget closing costs: Some lenders charge higher rates or fees for low down payments, which can shift the math significantly.
Frequently Asked Questions
Is it always better to invest instead of making a bigger down payment?
Not always. If your mortgage rate is higher than your expected after-tax investment return, paying down the mortgage wins. In a 7% mortgage environment, investing in bonds yielding 4–5% after tax doesn't beat the guaranteed interest savings. Equities might, but with more risk.
Does this calculator account for the mortgage interest tax deduction?
The base calculation doesn't include the mortgage interest deduction. If you itemize deductions, your effective mortgage rate is lower (multiply by 1 minus your tax rate). Adjust the mortgage rate input accordingly—for example, a 7% mortgage with a 25% tax bracket is effectively 5.25% if you itemize.
When does PMI go away in this calculator?
PMI is applied until your loan-to-value ratio drops below 80% (i.e., equity exceeds 20%). The calculator tracks this year by year using loan amortization and home appreciation, and stops applying PMI costs once that threshold is crossed.
What investment return should I use?
A conservative estimate for a diversified stock portfolio is 6–8% nominal (before taxes). After a 25% tax rate on gains, that's 4.5–6% effective. For bonds or balanced portfolios, use 3–5%. The tool lets you adjust this—try a few scenarios to see how sensitive the result is.