Extra Principal Payments
Small extras can shorten a long loan
An extra $200 a month against a mortgage feels like throwing pennies at a mountain. On a $340,000 loan at 6.5%, it removes more than six years from the term and saves over $100,000, which is a strange return for pennies.
Model it directly
The base loan is $340,000 at 6.5% for 30 years, which is about $2,149 a month and roughly $434,000 of total interest.
To model the extra, enter the same loan with a payment of $2,349 — the regular amount plus $200. The payoff moves in to about 23 years and eight months.
Total interest drops to roughly $327,000. The extra $200 a month saved about $106,000 and six and a half years of payments.
Why the effect is so disproportionate
Extra principal payments skip interest that would have been charged on that amount for the entire remaining term.
A $200 payment in year two avoids 28 years of compounding interest on that $200. The same $200 in year 25 avoids only five years of it.
That is why early extra payments matter far more than later ones, and why a modest amount started immediately beats a large amount started in a decade.
- Base loan: about $2,149 a month, roughly $434,000 in interest.
- With $200 extra: about 23 years 8 months, roughly $327,000 in interest.
- Early extra payments are worth far more than late ones.
- Extra payments shorten the term; they do not lower the required payment.
- One extra payment per year has a similar effect to spreading it monthly.
Three ways to do it
The simplest is adding a fixed amount to each monthly payment, which works well when your income is steady and predictable.
Biweekly payments — half the payment every two weeks — produce 26 half-payments, which equals 13 monthly payments a year. That one extra payment typically shaves four to five years off a 30-year loan.
The third option is one annual lump sum from a bonus or tax refund. It is less consistent but requires no monthly change, and for many households it is the version that actually happens.
Where the extra dollar does the most work
An extra principal payment is worth the most in the first few years of the loan, because that is when the balance is largest and every dollar removed avoids the most future interest.
On a $320,000 loan at 6.5%, a single extra $1,000 in year two removes roughly $2,400 of eventual interest. The same $1,000 in year twenty-two removes a few hundred.
This does not mean late extra payments are pointless, only that the early ones carry outsized weight. If you are going to be inconsistent about it, be consistent early.
It also argues against waiting until you feel financially comfortable. A modest extra amount starting now generally beats a larger amount starting in eight years.
Before you start, check two things
Make sure the servicer applies extra money to principal rather than to the next scheduled payment. Many require a specific designation, and getting this wrong means months of extra payments that did nothing.
Confirm there is no prepayment penalty. These are uncommon on standard conforming mortgages and worth verifying anyway.
Then weigh the alternative. At a 3% mortgage rate, investing the extra $200 almost certainly beats prepaying. At 6.5% or 7%, the guaranteed return from prepaying is genuinely competitive with expected market returns, and it comes with no volatility.
Try these inputs
- Base loan: $340,000, 6.5%, 30 years
- With $200 extra: model a $2,349 monthly payment
- With $500 extra: model a $2,649 monthly payment