Mortgage Remortgaging Calculator 2026 — How Much You Save Switching Bank
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Mortgage Remortgaging Calculator 2026
See how much you save by moving your mortgage to a new bank at zero cost
A surroga (mortgage portability, Legge Bersani – D.L. 7/2007) lets you move your mortgage to a new bank to get a better rate at no cost to you: the valuation, arrangement fees, notary and taxes are paid by the new bank, and there are no early-repayment penalties. The outstanding balance cannot go up (to borrow more you need a replacement mortgage, not a surroga). This tool compares your current payment with the payment at the new rate on the same balance, using a constant-payment (French) amortisation: it is an indicative estimate, not a quote. The real outcome depends on the actual TAN/TAEG of the new offer.
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Mortgage remortgaging (surroga): how it works and how much you can save
A surroga (mortgage portability) lets you move the mortgage you already have to another bank offering a lower rate, at no cost to you. The outstanding balance stays the same: what changes is the interest rate and, if you want, the term. This free tool compares the payment you make today with the one you would make at the new rate, and tells you how much you save each month and over the total interest. The calculation runs entirely in your browser: enter the outstanding balance, your current rate, the payments you have left and the new rate on offer.
How the saving is calculated
A mortgage payment is worked out using French amortisation (constant payment): for the same capital and term, the lower the rate, the lower the payment. The monthly payment formula is:
Payment = C × i ÷ [1 − (1 + i)−n]
where C is the outstanding balance, i is the monthly rate (the annual TAN divided by 12) and n is the number of payments left. The calculator applies this formula to your current mortgage and to the new rate, then compares the two payments and the two totals. Since the capital to repay is identical in both cases, the difference between the two totals is entirely interest cost: whatever you save (or pay extra) is all interest.
Worked example
A mortgage with an outstanding balance of €120,000, a current rate of 4.20% (TAN) and 240 payments left (20 years), remortgaged at a new rate of 2.80% keeping the same term:
| Item | Current mortgage | After remortgaging |
|---|---|---|
| Rate (TAN) | 4,20% | 2,80% |
| Monthly payment | 739,88 € | 653,57 € |
| Remaining interest total | 57.572 € | 36.856 € |
The saving is €86.32 a month and around €20,716 of interest over the whole remaining term. Because a surroga costs the borrower nothing, that saving is net. Change your own figures and the result shifts, which is why it is worth running the simulation on your real situation.
Zero-cost remortgaging: what the Bersani Act says
The fact that a surroga is free for the borrower is set out in the Bersani Act (Decree Law 7/2007, converted into Law 40/2007). The new bank picks up the valuation, arrangement work, notary fees and taxes, and you cannot be charged penalties or commission for the transfer. The only costs that remain yours are ones you chose independently, such as an optional insurance policy. In practice, if you find a lower rate, the benefit is not eaten up by set-up fees.
Watch the term: a lower payment is not always a saving
With a surroga you can also extend the term of the mortgage to bring the payment down further. That helps if you need breathing room in your monthly budget, but it has a downside: stretching the schedule means more payments and therefore more interest in total. The calculator shows this openly: enter a longer new term and you will see the payment fall, together with a warning that overall interest may rise. Conversely, shortening the term raises the payment but reduces total interest.
Frequently asked questions
How much does remortgaging cost?
Nothing for the borrower. Under the Bersani Act (Decree Law 7/2007) a surroga is free: valuation, arrangement work, notary fees and taxes are all paid by the new bank, which cannot charge you penalties or commission for the transfer. The saving you get on the rate is therefore net.
Can I borrow more than the outstanding balance with a surroga?
No. A surroga moves the existing mortgage to another bank keeping the same outstanding balance: you can change the rate and the term, but not increase the amount. If you need extra cash you need a replacement mortgage, which is a different transaction and does carry costs for you.
Is remortgaging worth it?
It is worth it whenever the new rate is lower than the one you pay today: since the transaction is free, every point off the rate turns into a lighter payment and less interest, with no upfront cost. It deserves more thought if you plan to stretch the term to cut the payment: the payment falls, but total interest can go up.
What do I need to calculate the saving?
Just four figures, all of which appear in your amortisation schedule or in the bank's statement: the outstanding balance (what you still have to repay), your current rate (TAN), how many payments are left and the new rate offered by the bank you want to move to. The new term is optional: leave it empty and the calculation keeps your current remaining payments.
Related tools: mortgage payment calculator, early repayment calculator, the guide to mortgage portability, the piece on when renegotiating your mortgage is worth it and the guide to financial calculators.
