One lender shows a lower rate. Another shows lower monthly payments. A third says the total borrowing cost is better. This is exactly why people get tripped up when working out how to compare mortgage illustrations. The paperwork looks official, the numbers look precise, and yet two deals that seem similar can lead to very different outcomes.
That is not an accident. Mortgage illustrations are useful, but they are not designed to make your choice easy. They are designed to disclose information. Your job is to compare the right figures in the right order, so you do not get seduced by a headline rate and miss the bigger cost.
How to compare mortgage illustrations without getting fooled
Start with one rule: never compare just the interest rate. That is the oldest trap in the book.
A mortgage illustration can include arrangement fees, valuation fees, incentive periods, revert rates, repayment charges and assumptions about term length. If you only look at the top-line rate or the monthly payment in year one, you can end up choosing a deal that costs more overall or boxes you in when your plans change.
The smart way to compare is to line up the key parts of each illustration and ask one question throughout: what will this deal actually cost me, given how long I expect to keep it?
That last bit matters. A two-year fix may look brilliant on paper, but if the fees are chunky and you are likely to remortgage again quickly, the saving can disappear. On the other hand, a deal with a slightly higher rate but lower fees may work better if your loan size is smaller. It depends on the size of your mortgage, your deposit, your plans and how flexible you need the deal to be.
The figures that matter most
Initial rate and follow-on rate
The initial rate is the one lenders love to advertise. It is the fixed, tracker or discounted rate for the incentive period. It matters, of course, but it is only one part of the picture.
The follow-on rate matters just as much. This is often the lender’s standard variable rate after the initial period ends. If you stay on it, your payments can jump sharply. A mortgage that looks cheap for two years may become expensive fast if you do nothing afterwards.
This does not mean a deal with a high follow-on rate is automatically bad, because many borrowers remortgage before reaching it. But you should still notice it. If there is any chance you may stay put longer than planned, this number stops being background noise and starts being real money.
Monthly payments
Monthly payments are useful, but only if you know what period they cover. Some illustrations show the payment during the initial deal and then the higher payment after the incentive ends. Compare both.
Also check whether you are comparing repayment mortgages with repayment mortgages. If one illustration is interest-only and another is capital repayment, the lower monthly figure tells you very little. You need like-for-like comparisons.
Fees
This is where expensive mistakes happen.
Arrangement fees, booking fees and product fees can wipe out the benefit of a lower rate, especially on smaller loan amounts. A deal that saves you a few pounds a month can still cost more if it comes with a large upfront fee.
Look at whether the fee is paid upfront or added to the loan. If it is added, you will pay interest on it too. That can make the deal dearer than it first appears.
Valuation and legal incentives also matter. A free valuation or free legals can tilt the numbers in favour of one lender over another. Ignore these extras and you are not doing a proper comparison.
The APRC
You will see the APRC on mortgage illustrations. This is the Annual Percentage Rate of Charge. It is meant to show the total annual cost of the mortgage, including certain fees, over the full term.
Useful? Yes. Perfect? No.
APRC can help when you are comparing broad cost differences, but it is based on assumptions, including what happens after the initial rate ends. If you are likely to remortgage in two or five years, the APRC may not reflect your real-world cost. Treat it as a reference point, not the final verdict.
How to compare mortgage illustrations based on your real plans
This is the part many borrowers skip, and it is where brokers earn their keep.
A mortgage is not just a product. It is a strategy. If you are buying your first home and stretching affordability, the best illustration might be the one that keeps payments stable. If you are remortgaging and planning to overpay aggressively, flexibility may beat a tiny rate saving. If you may move in two years, early repayment charges become a big deal.
So before choosing a deal, get clear on your own likely timeline. Are you planning to stay put? Upsize? Start a family? Change jobs? Pay lump sums off the mortgage? These are not side issues. They affect which illustration is actually best.
Early repayment charges
Check the early repayment charges carefully. If you repay or switch during the deal period, these penalties can be steep.
A mortgage with a strong initial rate can become a poor choice if you expect to move or remortgage early. Equally, if you are confident you will keep the deal for the full fixed period, the charges may matter less. Again, context beats guesswork.
Overpayment rules
Many borrowers want the option to overpay, particularly if they expect bonuses, inheritance or uneven self-employed income. The illustration should tell you what overpayments are allowed.
That flexibility has value. A deal that lets you chip away at the balance without penalty can save a significant amount of interest over time. If your goal is to become mortgage-free faster, that feature deserves proper weight.
Portability
If you might move house during the deal, see whether the mortgage is portable. That means you may be able to take it with you to a new property, subject to approval.
Portable does not always mean simple. The lender still reassesses affordability and the new property. But if moving is a real possibility, portability is worth checking rather than assuming.
Common mistakes borrowers make
The first mistake is chasing the cheapest monthly payment without asking why it is cheapest. Sometimes it is because the term is longer, which means paying more interest over time.
The second is ignoring fees because they feel like a one-off. They are not just admin costs. They are part of the total price.
The third is comparing illustrations from different dates without checking whether the assumptions are the same. Rates can move. Loan amounts can differ. Even a small change in loan-to-value can alter the products available.
The fourth is treating lender paperwork as neutral. It is accurate in a regulatory sense, but it is not there to point out which deal is stronger for your situation. That is your job, or your broker’s.
A simple way to judge two or three illustrations
If you are stuck between a small handful of options, compare them over the period you realistically expect to keep the mortgage deal. Add together the monthly payments during that period, the upfront fees, any incentives you would receive, and any costs that would be added to the loan.
Then weigh the flexibility. If one deal is only marginally cheaper but has harsher early repayment charges or weaker overpayment options, it may not be the better deal at all.
This is why proper advice matters. A lender can sell you its mortgage. An adviser should help you choose the right mortgage.
Mortgage Genius exists for exactly this reason – to cut through the noise, compare the true cost, and stop borrowers getting sold on the wrong numbers.
The best mortgage illustration is not always the cheapest one
That line annoys people because they want a simple winner. Fair enough. But mortgages are messy.
The best illustration is the one that fits your deposit, income, property, timescale and plans. Sometimes that is the lowest-cost option. Sometimes it is the deal with lower fees. Sometimes it is the one with stronger flexibility because life is not tidy and plans change.
If you remember one thing, make it this: compare the whole deal, not the headline. Lenders know borrowers fixate on the rate. You do not need to play that game.
A clear head beats a flashy illustration every time.
