Repayment Home Loan Calculator
Paying extra on a home loan works, but the size of the prize depends on details most calculators blur: how often you pay, whether the extra is added to every repayment, and whether an offset balance is quietly cutting your interest bill. This repayment home loan calculator simulates the loan period by period, so you can test monthly, fortnightly and weekly repayments, a recurring extra payment and an offset balance in any combination, and see the interest saved, the time saved and the payoff date for each.
Quick Answer
On a $400,000 loan at 6.5% over 30 years, the standard monthly payment is $2,528.27 and total interest is $510,177.95. Adding $500 to every monthly payment ends the loan in 19 years 5 months and saves $205,557.14 in interest. You can also track what percentage of a loan you have repaid once the loan is under way.
Key takeaways
- Fortnightly repayments (half the monthly amount, 26 times a year) are worth 13 monthly payments a year and cut this loan’s interest to $392,682.25 with no extra payment at all.
- The extra field is per repayment, not per month: $500 extra fortnightly is a far bigger commitment than $500 extra monthly.
- A constant $20,000 offset balance cuts the same loan’s interest to $407,535.36 while the money stays withdrawable.
- Extra payments only save interest if your servicer applies them to principal. Confirm that first.
- Quick Answer
- How to use this home loan repayment calculator
- The formula and the period-by-period simulation
- Worked example: $500 extra on a $400,000 loan
- What each repayment frequency really does
- The extra payment ladder: $250, $500, $1,000
- What an offset balance does to the same loan
- Read this before you overpay: three checks
- What competing calculators miss
- Frequently asked questions
How to use this home loan repayment calculator
Enter the loan amount, the contract rate and the term, then pick a repayment frequency and add any extra payment and offset balance. The pre-filled values are the worked example below, so the first click reproduces this article’s numbers exactly.
The tool first works out the standard monthly payment from your amount, rate and term, the same starting point a mortgage payment calculator gives you. It then converts that payment to your chosen frequency and simulates the loan one period at a time: interest is charged on the balance minus the offset, the rest of the payment cuts principal, and any extra is added on top. Two runs happen per click, one with your extra and one without, so the saved figures are a clean comparison.
Three reading notes. The extra amount is added to every repayment at the chosen frequency, so $500 at weekly means $500 a week. The offset balance is held constant, which suits a savings buffer you leave parked; a balance you spend down will save less. And the rate is held fixed for the whole term, so treat the output as a plan based on today’s rate, not a forecast.
The formula and the period-by-period simulation
The starting payment uses the standard amortization formula, M = P × r(1+r)n ÷ ((1+r)n − 1), where P is the loan amount, r is the monthly rate (annual rate ÷ 12) and n is the term in months. At a 0% rate the payment is simply P ÷ n.
Everything after that is simulation rather than a closed formula, because extra payments and offsets break the neat schedule. Each period, the tool charges interest on (balance − offset) at the period rate, applies the payment plus extra to principal, caps the final principal slice at the remaining balance, and stops when the balance reaches zero. That exact final payment is why the totals here match a full amortization schedule to the cent instead of landing a payment out.
Frequency conversion is where tools quietly differ. Fortnightly here is half the monthly payment, paid 26 times a year. Weekly is the monthly payment × 12 ÷ 52, paid 52 times, which keeps the yearly total equal to monthly. Those two definitions are not the same trick, and the table below keeps them separate.
Worked example: $500 extra on a $400,000 loan
A $400,000 loan at 6.5% over 30 years, monthly repayments, an extra $500 a month and no offset produces these figures, every one reproduced by the tool above:
| Figure | No extra | With $500 extra |
|---|---|---|
| Monthly payment | $2,528.27 | $3,028.27 |
| Payoff time | 30 years | 19 years 5 months (233 months) |
| Total paid | $910,177.95 | $704,620.81 |
| Total interest | $510,177.95 | $304,620.81 |
The extra payments themselves total $116,500 across the shortened term, yet they remove $205,557.14 of interest and 127 months of payments. That gap is the whole argument for starting early: principal removed in the first years stops interest being charged on it for decades.
What each repayment frequency really does
Frequency changes the result through two different mechanisms, and only one of them is real acceleration. Fortnightly pays 13 monthly equivalents a year; weekly, as defined here, pays 12 but charges interest more often on a falling balance.
| Frequency (no extra, no offset) | Payment | Total interest | Payoff |
|---|---|---|---|
| Monthly (12 per year) | $2,528.27 | $510,177.95 | 30 years |
| Fortnightly (26 per year) | $1,264.14 | $392,682.25 | 24 years 2 months |
| Weekly (52 per year) | $583.45 | $508,289.03 | 29 years 11 months |
Two warnings follow from those numbers. First, some lenders set a fortnightly payment as the monthly amount × 12 ÷ 26, which pays the same per year as monthly and quietly deletes the $117,495.70 advantage shown above; check which definition your lender uses before counting the saving. Second, the often-quoted claim that weekly is nearly as powerful as fortnightly is wrong on this math: weekly alone saves $1,888.92, fortnightly saves $117,495.70.
The extra payment ladder: $250, $500, $1,000
Bigger extras save more interest, but with shrinking returns per dollar, because each step has fewer years of interest left to remove. These are monthly runs on the same $400,000 loan at 6.5%:
Doubling the extra from $250 to $500 adds $73,771.30 of savings and cuts the payoff from 23 years 5 months to 19 years 5 months. Doubling again to $1,000 adds $82,739.74 and reaches 14 years 9 months. The practical reading: the first sustainable extra matters most, so pick an amount you can keep paying in a bad month rather than a heroic one you abandon.
What an offset balance does to the same loan
An offset balance cuts interest without locking the money away, because interest is charged on the loan balance minus the offset. A constant $20,000 offset on the worked example loan, with no extra payments, cuts total interest from $510,177.95 to $407,535.36 and shortens the loan to 26 years 8 months.
That $102,642.59 saving is why an offset mortgage calculator is worth running before you commit spare cash to principal: money in offset keeps its flexibility, and the interest it saves is not taxed the way savings account interest is in many jurisdictions. The catch in this model is the constant-balance assumption. If the offset holds your emergency fund and it dips for a few months, the real saving lands somewhere below the figure shown.
Read this before you overpay: three checks
Extra payments are powerful, and three checks decide whether you actually collect the benefit. None of them is in the calculator, because all three live in your loan contract and your budget.
- Confirm the extra goes to principal. Some servicers apply overpayments to future scheduled payments, which saves nothing. Designate extra payments as principal-only and verify the balance on the next statement, as the CFPB advises borrowers to do.
- Check for prepayment penalties and fixed-loan caps. Most modern variable loans allow unlimited extra payments, but fixed loans often cap them or charge break costs. One look at the loan terms settles it before you send money.
- Compare against your other options honestly. An extra payment earns a guaranteed, risk-free return equal to your loan rate. That beats most alternatives at 6.5%; at a 3% rate with expensive card debt elsewhere, the same dollars may do more good on the card. An overpay mortgage calculator comparison plus a look at your highest-rate debt gives the full picture.
What competing calculators miss
Bank extra-repayment tools such as Virgin Money’s (run by InfoChoice) model extra payments well but stay inside one lender’s assumptions, and most show monthly schedules only. Australian repayment sites cover fortnightly and offset, yet several quote fortnightly gains with the lender conversion (monthly × 12 ÷ 26) that removes the extra annual payment, or round the worked example so loosely that the numbers cannot be checked. Overpayment tools that add lump sums and charts rarely model an offset balance at all.
This page’s differences are specific: all three frequencies plus extra plus offset in one simulation, a same-frequency baseline so gains are never double counted, an exact final payment, and worked examples you can reproduce to the cent in the tool above, including the corrected fortnightly figures (payment $1,264.14 at 6.5%, not the $790.09 figure an earlier version of this page printed for a different, unstated rate).
Frequently asked questions
Yes, when each fortnightly payment is half the monthly payment. You make 26 payments a year, equal to 13 monthly payments instead of 12, so one extra monthly payment reaches principal every year. On a $400,000 loan at 6.5% over 30 years, fortnightly payments of $1,264.14 cut total interest from $510,177.95 to $392,682.25 and end the loan in 24 years 2 months.
The tool subtracts your offset balance from the loan balance before charging interest each period, so the balance you pay interest on is smaller while the money stays available to withdraw. A $20,000 offset on the worked example loan cuts total interest to $407,535.36 and shortens the loan to 26 years 8 months, even with no extra payments. The model holds the offset balance constant for the whole term.
Only slightly, and the reason is in how this tool builds the weekly payment: it is the monthly payment times 12, divided by 52, so you pay the same total per year as monthly. On the worked example loan, weekly payments alone cut interest from $510,177.95 to $508,289.03 and finish one month early. Fortnightly is the bigger jump because half a monthly payment 26 times a year adds up to 13 monthly payments.
It depends on the rate, balance and extra amount, and the savings grow faster than the extra payments themselves. On a $400,000 loan at 6.5% over 30 years, an extra $500 a month saves $205,557.14 in interest and ends the loan 10 years 7 months early. An extra $250 a month still saves $131,785.84.
They should go entirely to principal, but only if your servicer applies them that way. Tell the servicer the extra is a principal-only payment and check the next statement to confirm the balance dropped by the full extra amount. If the servicer instead advances your due date, you save little or no interest.
Earlier money wins: a dollar of principal removed in year 1 avoids interest for the rest of the loan, so regular monthly extras beat an equal lump sum paid later. This tool models a recurring extra added to every repayment; it has no lump-sum field, so for a one-off payment, compare the timing honestly rather than treating the two as identical.
On a $300,000 loan at 6.5% over 30 years, an extra $200 a month saves $103,448.79 in interest and ends the loan 6 years 11 months early, in 23 years 1 month. Enter your own balance and rate above for the exact figure on your loan.
It can cause a small, temporary dip, because closing the loan removes an active installment account and narrows your credit mix. The effect is minor next to the interest saved, and scores typically recover within a few months as long as your other accounts stay in good standing.
Yes, and the calculator handles a 0% rate: extra payments shorten the term but save no interest, because there is none. A $120,000 loan at 0% over 10 years with an extra $100 a month finishes 10 months early, with interest saved of $0.00.
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References
- Consumer Financial Protection Bureau. Regulation Z High-Cost Mortgage Amendments, 12 CFR Part 1026 (prepayment penalty limits and payoff statement rules for home loans). Accessed October 24, 2026.
- Internal Revenue Service. Publication 936, Home Mortgage Interest Deduction (what counts as home mortgage interest and qualified loan limits). Accessed October 24, 2026.
- Board of Governors of the Federal Reserve System. Consumer Handbook on Adjustable-Rate Mortgages (how mortgage interest, payments and rate adjustments work). Accessed October 24, 2026.
- Australian Securities and Investments Commission, Moneysmart. Mortgage Calculator (repayment and total interest modelling for home loans). Accessed October 24, 2026.
- Australian Securities and Investments Commission, Moneysmart. Pay Off Your Mortgage Faster (extra repayments, lump sums and frequency changes). Accessed October 24, 2026.
- Australian Securities and Investments Commission, Moneysmart. Offset Accounts (how an offset balance reduces the interest charged on a home loan). Accessed October 24, 2026.
- Experian. Should I Pay Extra on My Mortgage Each Month? (opportunity cost, prepayment penalties and emergency-fund trade-offs). Accessed October 24, 2026.
- Consumer Financial Protection Bureau. Owning a Home: Tools and Resources for Homebuyers (mortgage payment, amortization and servicer guidance hub). Accessed October 24, 2026.