How a $6,781.69 Extra Payment Eliminated $36,318.51 in Interest
The same principal-prepayment strategy applied to a $1,000,000 mortgage. Any loan amount can benefit; the idea scales up or down.
Example calculation. Actual savings vary by loan terms, interest rate, and payment timing.
The Idea in One Sentence
Every mortgage payment is split into interest (money the bank keeps) and principal (money that reduces what you owe). If you send one extra payment that goes 100% to principal, you don't just pay down the loan; you skip the interest that would have been charged on those months. That interest is gone forever.
The Loan; terms
- Loan amount
- $1,000,000
- Interest rate
- 6.25%
- Term
- 30 years (360 months)
- Regular monthly payment
- $6,157.17
- First payment date
- March 1, 2026
What She Did; step by step
Made the regular first payment on time.
On March 1, 2026, she paid the normal scheduled amount of $6,157.17; the ordinary first monthly payment on the loan.
Looked ahead on the amortization schedule.
She added the Principal column for the next 7 months (April–October 2026, green below): $953.78 + $958.75 + $963.74 + $968.76 + $973.81 + $978.88 + $983.98 = $6,781.69.
Sent one additional principal-only payment.
Right after the March payment, she sent the bank a single additional payment of $6,781.69; the total principal scheduled across the next 7 months.
Labeled the payment clearly.
On the payment memo she wrote: "Apply to principal only." This tells the bank the money must reduce the loan balance directly; it is not a prepayment of a future monthly bill.
The bank skipped ahead 7 months on the schedule.
Because the principal for months 2 through 8 was fully paid, the interest for those 7 months was never charged. The next interest calculation began from the new, lower balance, and the loan finishes 7 months earlier.
The Payment Schedule; What to Look At
Below are the first months of the loan. The Principal column (in green) is what you add up to build your one-time extra payment. The Interest column (in amber) is what disappears when that principal is prepaid.
| Month | Payment | Interest | Principal | Loan Balance |
|---|---|---|---|---|
| Mar 2026 | $6,157.17 | $5,208.33 | $948.84 | $1,000,000 |
| Apr 2026 | $6,157.17 | $5,203.39 | $953.78 | $999,051 |
| May 2026 | $6,157.17 | $5,198.42 | $958.75 | $998,097 |
| Jun 2026 | $6,157.17 | $5,193.43 | $963.74 | $997,139 |
| Jul 2026 | $6,157.17 | $5,188.41 | $968.76 | $996,175 |
| Aug 2026 | $6,157.17 | $5,183.37 | $973.81 | $995,206 |
| Sep 2026 | $6,157.17 | $5,178.29 | $978.88 | $994,232 |
| Oct 2026 | $6,157.17 | $5,173.20 | $983.98 | $993,253 |
| Nov 2026 | $6,157.17 | $5,168.07 | $989.10 | $992,269 |
| Totals for the 7 green months | $36,318.51 | $6,781.69 | ||
Sample from the illustrative amortization schedule. Full 360-month schedule available on request. Loan balances rounded to the nearest dollar for display.
Result: one $6,781.69 payment eliminated $36,318.51 of future interest.
By prepaying the principal for months 2 through 8 (April through October 2026), those seven months of interest charges were never applied to the loan. The bank shifted the schedule forward, and the loan will finish 7 months earlier than the original 30-year term.
The Strategy Scales to Any Loan
Whether your mortgage is $200,000, $500,000, $1,000,000, or more, the math works the same way. Interest is charged on the outstanding balance every month, and in the early years of a loan almost every dollar of your regular payment goes to interest; only a small amount goes to principal.
When you send an extra payment labeled "principal only," you skip past those small-principal months in one shot. On a $1M loan, one $6,781.69 payment eliminates $36,318.51 of interest. On a $1.7M loan, one $11,258.48 payment eliminates $62,982.04. See that example. Same idea, different scale.
How To Apply This Strategy to Your Own Loan
Get your full amortization schedule
It lists every month of the loan and how each payment splits between interest and principal. Mortgage Vault generates this automatically the moment you enter your loan details.
Decide how many months of principal to prepay
3 months, 5 months, 7 months, or 12 months; whatever fits your budget. Add those principal amounts together. That total is your one-time extra payment.
Send the extra payment as a separate transaction
Do not combine it with your regular monthly payment. Send it as its own payment so the bank does not mistake it for next month's bill.
Label it clearly
In the memo or online-payment note write: "Apply to principal only." After it posts, check your next statement to confirm the balance dropped by the full amount.
Repeat whenever you can
Once, once a year, or every month. Every extra dollar directed to principal early in the loan removes many dollars of future interest.
Before you do this; three things to confirm with your lender
- Your loan has no prepayment penalty (most U.S. residential mortgages don't, but always check).
- The lender accepts principal-only payments and has a clear way to designate them (online, by check memo, or by phone).
- You keep a healthy emergency fund. Once money goes to principal, it is not easily taken back; you can't call the bank and ask for it as cash.
How Mortgage Vault Helps
Mortgage Vault builds your full amortization schedule, shows you exactly which months to target, and calculates the interest you eliminate with each principal-only payment. Whether your loan is $100,000 or $10,000,000, the tool does the math and keeps the records. Every dollar you save is a dollar the bank doesn't.
This is an illustrative example. Actual savings depend on your loan terms, interest rate, and lender policies. This document is educational and does not constitute financial, tax, or legal advice. Please review your loan agreement or consult a licensed professional before changing your payment strategy.