What are extra mortgage payments?
Key takeaways
04 · ideas- Extra payments go directly to principal, not interest
- $300/month extra on a $200k loan saves $86,000 in interest
- Start early — extra payments are most valuable in year 1
- Even $50/month extra makes a meaningful difference
Basic level
The essentials · 1 min
An extra mortgage payment is any amount you pay beyond your required monthly payment. When you pay extra, that money goes directly to reducing your loan balance (principal) — not to interest.
Why does this matter? Because mortgage interest is calculated as a percentage of your remaining balance. A lower balance means less interest accrues each month. Less interest means more of your regular payment reduces principal. This creates a snowball effect that accelerates payoff dramatically.
A simple example:- Loan: $200,000 at 7.5% for 30 years
- Regular payment: $1,398/month
- Total interest without extra payments: $303,000
- Add $300/month extra: total interest drops to $217,000 — saving $86,000 and cutting 8 years off the loan
Intermediate level
How it applies · 2 min
How extra payments reduce your balance
Each month, your interest is calculated as: balance × (annual rate ÷ 12)
On a $200,000 balance at 7.5%: $200,000 × (0.075 ÷ 12) = $1,250 in interest
Of your $1,398 payment, only $148 reduces the principal. That's why the loan takes 30 years to pay off.
Now add $300 extra. Your payment becomes $1,698. The same $1,250 goes to interest, but now $448 reduces principal — 3x more paydown per month. As the balance drops faster, next month's interest is slightly less, freeing even more to reduce principal.
Comparison table — $200,000 at 7.5%, 30-year:
| Extra monthly | Payoff time | Interest saved | Total interest |
|---|---|---|---|
| $0 | 360 months | $0 | $303,434 |
| $100 | 330 months | $43,000 | $260,000 |
| $300 | 278 months | $86,000 | $217,000 |
| $500 | 244 months | $121,700 | $181,000 |
| $1,000 | 196 months | $171,000 | $132,000 |
Timing matters
Extra payments made early in the loan — when the balance is large — have maximum impact. A $10,000 payment in month 1 eliminates roughly $10,000 of high-interest balance, preventing 30 years of interest on that amount.
The same $10,000 paid in year 25 when you only owe $40,000 helps much less, because you're already paying mostly principal by that point.
Best sources of extra payments:- Annual bonus or 13th-month salary
- Tax refund
- Small regular increases ($50–$100/month on each raise)
- Rounding up to the nearest $50 or $100
Advanced level
The math, step by step · 1 min
The math behind the snowball effect
The acceleration works because of how amortization interacts with extra payments.
In standard amortization, monthly payment M on principal P, rate r per period, n periods:
With extra payment E per month, the effective period count drops to n' where:
For our example: P = 200,000, r = 0.00625, M = 1,398, E = 300:
Key insight: The $300/month extra over 278 months = $83,400 invested in the loan, but saves $86,000 in interest — an immediate positive return. The effective an equivalent return at your loan rate (without market risk) rate equals your mortgage rate (7.5% in this case).