Making an extra principal payment can save you thousands over the life of your mortgage
Making one extra mortgage payment per year can save a Lake County homeowner with a $393,636 loan over $50,000 in interest and shave roughly 5 years off a 30-year term. The math is simple: when you pay down principal faster, you reduce the balance on which daily interest compounds, and the savings compound right back at you. But the strategy matters — how you structure those extra payments, whether your lender allows them, and whether paying down your mortgage beats investing the same money all affect the right answer for your family.
How much does one extra payment really save you?
Let's ground this in a real Lake County number. The average home value in Lake County is $393,636 as of July 2026 (Zillow). The current national average 30-year fixed rate is 6.78% (LendingTree). On a loan at that rate, every extra dollar you send to principal earns a guaranteed 6.78% return by reducing future interest — no market risk, no tax on the gain.
Make one extra payment per year directed entirely to principal, and you can cut the loan term by roughly 5 years and save tens of thousands in interest. The exact savings depend on your loan balance and rate, but the principle is always the same: the earlier you pay down principal, the more interest you avoid.
What are your best strategies for extra payments?
You have three main levers to pull, and each fits a different financial style.
The 1/12th rule — add 1/12th of your monthly payment to every regular payment. Divide your $2,050 payment by 12 (about $170), add that to each monthly check, and you've made the equivalent of one extra full payment by year's end. This is the most painless method because spread across 12 months, the extra $170 barely registers in most budgets.
The lump-sum approach — send a bonus, tax refund, or year-end surplus directly to principal. The IRS issued an average refund of roughly $3,000 in 2025. A single $3,000 lump sum applied to principal in year one of a $315,000 loan at 6.78% saves about $20,000 in interest over the life of the loan. The key is writing "principal-only payment" clearly on the check or selecting that option in your online portal — otherwise, the lender may apply it as a prepayment of future interest.
Biweekly payments — pay half your monthly payment every two weeks. Because there are 52 weeks in a year, you make 26 half-payments, which equals 13 full payments per year. The extra payment automatically goes to principal. Some lenders offer this as a free program; others charge a setup fee (Bankrate).
What traps should you avoid?
Not all lenders handle extra payments the same way. Before you send a dime, confirm three things.
First, verify your lender applies principal-only payments correctly. Some lenders may hold partial payments until they equal a full monthly payment, rather than applying them immediately (Rocket Mortgage). Always call your servicer and ask how to ensure extra payments go to principal only, not to future interest.
Second, check for prepayment penalties. While most conventional loans no longer carry them, some subprime or non-QM loans still do. A prepayment penalty can wipe out your interest savings if you pay off the loan too quickly. Your loan estimate from closing documents lists this under "Prepayment Penalty."
Third, watch third-party biweekly services. Some companies offer to set up biweekly drafts from your bank account for a fee. The Bankrate guide notes that some lenders may charge enrollment fees that eat into your savings (Bankrate). Your lender may offer a free automated biweekly option — ask before paying a third party.
Is paying down your mortgage better than investing?
This is the question that splits financial advisors. Paying down a 6.78% mortgage is a guaranteed return — dollar for dollar, you save exactly 6.78% on every extra payment. The S&P 500 has historically returned about 10% annually, but that return is not guaranteed. In any given year, the market could drop 20% while your mortgage keeps compounding at 6.78%.
Here's a framework for Illinois homeowners: if you have high-interest credit card debt (20%+ APR), pay that first. If you don't have a 3-6 month emergency fund, build that before sending extra to the mortgage. If you're maxing out your 401(k) match at work, the math tilts toward investing the difference. According to the Freedom Mortgage guide on prepayment, accelerating principal payments works best when you have stable cash flow and no higher-interest debt (Freedom Mortgage). But if you have a stable job, a healthy emergency fund, and the psychological peace of mind that comes from owning your home free and clear is worth something, paying extra principal is a strong play.
For Illinois residents, mortgage interest is deductible on federal taxes only if you itemize — and since the standard deduction roughly doubled in 2018, fewer homeowners itemize than before. That means your effective after-tax rate on the mortgage is likely very close to 6.78%, making the prepayment math even more favorable. The current LendingTree data shows 30-year rates at 6.78% (LendingTree), so every extra dollar you pay effectively earns that return — tax-free.
Tax implications for Illinois homeowners
Mortgage interest is deductible on your federal return if you itemize deductions. For 2026, the standard deduction for married couples filing jointly is roughly $30,000 and $15,000 for single filers. Given that the average Lake County home value is $393,636, the mortgage interest on a $315,000 loan at 6.78% is about $21,000 in year one — below the standard deduction threshold for most couples. That means most Illinois homeowners will not benefit from the mortgage interest deduction, making the effective after-tax cost of your mortgage very close to the stated 6.78%.
Illinois state income tax does not allow a deduction for mortgage interest, so there is no state-level benefit to carrying a large balance. This further tilts the math toward paying down principal rather than keeping the loan for the tax break.
Checklist before your first extra payment
Before you send a single dollar beyond your regular payment, run through this checklist:
Call your lender. Ask whether they accept principal-only payments, whether they offer automatic biweekly drafts, and whether any fees apply (Rocket Mortgage recommends checking with your lender first, as not all lenders permit principal-only payments). Review your loan documents. Check for a prepayment penalty clause. If you have a conventional loan originated after 2014, you almost certainly have none, but verify with your servicer. Align your budget. Make sure you have a 3-6 month emergency fund and are contributing enough to earn your full employer 401(k) match before accelerating mortgage payments. Decide your method. Monthly 1/12th additions, biweekly payments, or annual lump sums — pick the one you will actually stick with. Set a reminder. If you are not automating, mark your calendar. Consistency is what delivers the savings.
