Prepaying your home loan: How extra payments cut interest (and balance transfers, honestly assessed)

When I run the numbers on a $350,000 home loan at 6.75%, one line always surprises people: adding $200 a month to the payment — less than many households spend on takeout — removes $114,979.91 of interest and ends the loan 6 years and 3 months early. In this guide I show the full prepayment table, explain where the extra money actually goes, and then give the home loan balance transfer the same honest treatment, including the version of it that quietly costs you more.

The prepayment math on a $350,000 loan

The base loan: $350,000 at 6.75% fixed for 30 years. The standard payment is $2,270.09 a month, and if you make exactly that payment 360 times you hand over $467,236.25 in interest — comfortably more than the house cost you borrowed. Now I add a fixed extra amount to every payment and let the loan end whenever the balance hits zero:

Cent-exact amortization: interest is charged monthly on the remaining balance, and each extra dollar reduces principal immediately. The final payment in each prepayment row is smaller than usual because the balance runs out mid-payment.

Why is the effect so outsized? Because in the early years almost all of your standard payment is interest. On this loan your first payment is $1,968.75 of interest and only $301.34 of principal. An extra $200 nearly doubles the principal portion of that payment — and every dollar of principal removed in month one is a dollar that would otherwise have been charged interest 359 more times.

Where the extra money goes: the balance gap

Another way I like to show prepayment is the balance gap — how much less you owe at each milestone if you add $200 a month:

The gap compounds because a lower balance means less interest inside each standard payment, so more of the standard payment attacks principal too. Prepayment feeds on itself.

That growing gap is also why prepayment is such powerful protection if you sell or refinance mid-loan: at year 10 the prepayer has $34,144.78 more equity from exactly the same house and the same initial loan.

Modelling it yourself: an EMI calculator with prepayment

People often search for a home loan emi calculator with prepayment built in, and the honest truth is that the job splits into two steps any home loan prepayment calculator also performs. First, get your base payment: enter your loan, rate and term in our Home Loan EMI Calculator. Second, take that payment into the Amortization Calculator, add your extra monthly amount, and watch the payoff date and total interest move. I run the two-step version because it shows the month-by-month schedule — you can see the exact payment where your balance crosses below any target, which is the detail that matters for the balance-transfer decision below.

Lump sums work too — if they land on principal

Monthly extras are not the only shape prepayment takes. A tax refund, a bonus or an inheritance can do the same job in one hit. On this article’s loan, a single $10,000 extra payment made at month 12 — with nothing extra before or after — cuts total interest from $467,236.25 to $412,138.62, a saving of $55,097.63, and ends the loan at payment 332, two years and four months early. The earlier the lump lands, the harder it works, because it stops interest accruing on that $10,000 for every remaining month.

Two practical details decide whether you actually get that saving. First, tell your servicer in writing that the extra amount is to be applied to principal; without instructions, some servicers treat an overpayment as next month’s payment paid early, which saves you almost nothing. Second, check your loan documents for a prepayment penalty. They are rare on modern US mortgages and generally absent on loans more than a few years old, but “rare” is not “never” — one sentence in your note or closing disclosure settles it. And keep your emergency fund intact: principal you have prepaid is equity, not cash, and you cannot easily borrow it back in a crisis.

Home loan balance transfer: the break-even test

A home loan balance transfer — refinancing in US terms — means replacing your current loan with a new one at a lower rate, usually for a fee. Any home loan balance transfer calculator is really answering one question: do the savings outrun the costs before you move or refinance again? Let me work the example on this article’s loan. Five years in, the balance is $328,565.22 and you have already paid $114,770.62 of interest. A lender offers 5.75% for the remaining 25 years, with $6,500 of closing costs:

Same balance, same finish date. The transfer saves $203.07 a month and $54,421.60 overall after closing costs.

The break-even point is the moment the monthly savings repay the closing costs: $6,500 ÷ $203.07 ≈ 32 months, so the transfer moves into profit in month 33. Stay in the new loan well beyond that and the transfer is a clear win; sell the house in year two and you paid $6,500 to save about $4,874 — a loss dressed as a lower rate. That one division is the whole discipline of balance transfers.

My rule after running these numbers for years: prepay first if your rate is already competitive, and transfer only when the rate drop is at least three-quarters of a point, the term does not restart, and your break-even lands comfortably inside how long you realistically expect to keep the loan.

Sources: Consumer Financial Protection Bureau (CFPB) guidance on refinancing and closing costs. Rates are illustrative; every schedule, balance and interest figure was recomputed month by month from the standard amortization formula.