Extra payments vs. investing
Key takeaways
04 · ideas- Paying mortgage at 7.5% = 7.5% equivalent at loan rate return, tax-free growth
- S&P 500 averages ~10% nominal, ~7% real — but with volatility
- 401(k) match always wins first — it's an instant 50-100% return
- The right answer depends on your rate, tax situation, and risk tolerance
Basic level
The essentials · 1 min
If you have $500 extra per month, should you pay down your mortgage faster or invest it?
The short answer: it depends on your mortgage rate compared to what you'd earn investing.
- If your mortgage rate is higher than expected investment returns → pay mortgage
- If your mortgage rate is lower → invest
- If they're roughly equal → personal preference wins
But first: prioritize capturing any 401(k) employer match before either. A 100% employer match is a guaranteed 100% instant return — nothing beats that.
Simple rule of thumb:- Mortgage rate > 7%: pay down mortgage
- Mortgage rate < 4%: invest the difference
- Mortgage rate 4–7%: both are reasonable, choose based on psychology
Intermediate level
How it applies · 2 min
**Note on US-specific references:** This article mentions 401(k), IRA, and Roth accounts — retirement account types specific to the United States tax system. If you're based outside the US, equivalent vehicles exist in your country (e.g., RRSP in Canada, ISA in the UK, Superannuation in Australia, AFORE in Mexico). The mathematical principles discussed apply universally; the specific account names are illustrative.
The real comparison
Paying down mortgage at 7.5%:- Guaranteed 7.5% return
- Risk-free (no market volatility)
- Tax implications vary — mortgage interest may be deductible if you itemize
- Benefit: psychological security, no debt
- Expected return higher, but variable — some years will be -30%
- Tax drag from dividends and capital gains
- Benefit: liquidity (can access money), potential for higher returns
The 30-year comparison on $500/month:
| Strategy | 30-year outcome |
|---|---|
| Mortgage paydown (7.5% saved) | ~$220,000 in interest saved, mortgage paid off ~8 years early |
| Invested at 8% (taxable) | ~$680,000 portfolio |
| Invested in Roth IRA at 8% | ~$680,000 tax-free |
Investing clearly wins on raw numbers — but the mortgage paydown is risk-free and certain. The investment portfolio could be worth $1.2M or $200K depending on timing.
The order of priorities
Most financial planners recommend this sequence:- Emergency fund (3–6 months expenses in HYSA)
- 401(k) up to full employer match
- High-interest debt (> 7–8% APR) — includes most credit cards
- Roth IRA or HSA max
- Max 401(k)
- Then: mortgage paydown vs. taxable investing
Mortgage vs. investing is a step 6 decision, not a first priority.
Advanced level
The math, step by step · 2 min
After-tax rate comparison
The decision is: pay mortgage at rate r_m or invest at after-tax return r_i.
After-tax investment return depends on account type:- Taxable brokerage: $r_i = r_{pre} \times (1 - \text{marginal rate})$, roughly
- Roth IRA: $r_i = r_{pre}$ (no tax drag on growth)
- Traditional 401(k): $r_i \approx r_{pre}$ during accumulation, taxed on withdrawal
- If you itemize (rare after 2017 TCJA expanded standard deduction): $r_m = r_{nominal} \times (1 - \text{marginal rate})$
- If standard deduction (most people): $r_m = r_{nominal}$ — no tax benefit
- Mortgage effective rate: 7.5% (no deduction if standard deduction)
- Taxable account at 10% nominal: ~8.1% after-tax (long-term cap gains rate)
- Roth IRA at 10%: full 10% — beats mortgage clearly
Sequence of returns matters: The psychological argument for paying off the mortgage is strongest for people approaching retirement. A paid-off home removes a fixed obligation, reducing the risk of being forced to sell investments in a down market to make mortgage payments.
For r_m = 7.5\% and r_i = 8\%: the crossover happens very early — investing wins after year 3 in expectation, but the variance of investing creates a ~20% probability of mortgage paydown winning over any 30-year period.