Estimate your monthly mortgage costs
This is a guide only. It does not replace a formal mortgage illustration or lender affordability checks.
How this first direct mortgage calculator helps
If you are comparing first direct home loan options, this calculator gives you a quick estimate of monthly payments, total interest, and the impact of adding fees or overpaying. It is designed for UK-style mortgage planning, where borrowers often need to compare repayment mortgages against interest-only structures and decide whether product fees should be paid upfront or added to the loan.
A good estimate can help you answer practical questions before speaking to an adviser:
- Can I comfortably afford the monthly payment at this rate?
- How much extra interest will I pay if I add fees to the loan?
- What difference does a monthly overpayment actually make?
- How does an interest-only structure affect my total cost and final balance?
What the calculator includes
1) Repayment mortgage estimate
For a repayment mortgage, the calculator uses the standard amortisation formula. Each monthly payment includes interest and a portion of capital, so your balance reduces over time. You also get an estimated loan payoff timeline if you enter a monthly overpayment.
2) Interest-only estimate
For interest-only, the calculator estimates monthly interest payments based on the current balance. If you include overpayments, it assumes those overpayments reduce capital. At the end of the term, any remaining mortgage balance is shown as a lump sum that still needs to be repaid.
3) Fee treatment
You can model arrangement fees in two ways:
- Pay upfront: does not increase your loan balance, but you need more cash now.
- Add to loan: increases monthly payments and total interest paid over the term.
How to use the calculator effectively
- Enter your expected mortgage amount and annual interest rate.
- Choose your term length and repayment type.
- Add any fee and decide whether to add it to the mortgage balance.
- Test overpayment scenarios (for example, £50, £100, and £200 per month).
- Compare results and stress-test affordability.
If you are buying with a higher loan-to-value (LTV), enter property value too. LTV helps frame risk and can influence the products and rates available.
Repayment vs interest-only: quick comparison
Repayment mortgage
- Higher monthly payment than interest-only (usually).
- Balance falls every month.
- No large capital balance to clear at the end, assuming full term completion.
Interest-only mortgage
- Lower monthly payment in many cases.
- Mortgage balance does not automatically clear.
- You must have a credible repayment strategy for the remaining capital at term end.
Important real-world factors not fully captured
Any online mortgage tool is a simplified model. Before making a decision, account for:
- Product expiry and remortgage risk after fixed or discounted periods.
- Early repayment charges (ERCs) if you overpay above product limits.
- Valuation fees, legal costs, broker fees, and moving expenses.
- Changes in household income, childcare costs, or other debt commitments.
- Lender stress testing and affordability assessments, which may differ from simple payment math.
Overpayment strategy: small amounts can matter
A steady overpayment can significantly reduce total interest on a repayment mortgage. Even modest extra payments can shorten the term, especially in the early years when interest makes up a larger share of each instalment. If your product allows penalty-free overpayments up to a limit, this can be an efficient way to reduce long-term borrowing cost.
Always confirm overpayment rules in your mortgage offer, because exceeding permitted limits may trigger charges.
Frequently asked questions
Is this an official first direct calculator?
No. This is an independent educational tool designed to estimate payments and compare scenarios.
Does this calculator include insurance, tax, or service charges?
No. Results focus on mortgage repayment mechanics only. Add buildings insurance, life cover, and other household costs separately in your full budget.
Can rates change during the term?
Yes. If you are not on a fixed rate for the full term, your payment can change. Re-run the calculator with higher and lower rates to test sensitivity.
Final thought
Use this first direct mortgage calculator as a decision support tool, not a final lending decision. The best approach is to pair these numbers with a detailed household budget and a formal mortgage illustration from your lender or adviser. That combination gives you both mathematical clarity and product-specific accuracy.