About this calculator
The Refinance Calculator compares an existing loan or mortgage with a new deal by estimating payment changes, interest savings, fees, break-even time, and total cost. It is useful when deciding whether a lower rate is worth arrangement fees, valuation fees, legal costs, or early repayment charges. Use this expanded guide when you need more than a quick result. It explains the assumptions behind the Refinance Calculator, the records to gather, and the decisions the estimate can support. It is especially useful for borrowers comparing an existing loan or mortgage with a new deal, especially where rates, fees, early repayment charges, or terms differ. The strongest use of the page is scenario comparison: change one input at a time, compare the output, and keep a note of which assumption changed.
Refinance comparison method
The calculator compares remaining cost on the current deal with projected cost on the new deal, including upfront or rolled-in fees. The calculator result depends on the quality of the inputs and on the rule set or formula selected in the calculator above. For practical use, treat the output as a structured estimate: start with the core inputs, review the main outputs, then test the decision points that matter most to your situation. Key decisions include whether monthly savings recover switching costs, whether a longer term hides higher total interest, whether fees should be paid upfront or added to the loan.
- monthly saving = current payment - new payment
- break-even months = refinance costs / monthly saving
- net saving = old total cost - new total cost - fees
- better estimate = accurate inputs + correct rule set + realistic assumptions
- scenario difference = revised result - original result
How to use the refinance calculator
- Enter the current balance, rate, payment, and remaining term.
- Enter the new rate, term, and expected payment type.
- Add arrangement fees, legal fees, valuation fees, and early repayment charges.
- Review the new monthly payment and total cost comparison.
- Check the break-even point before deciding whether switching is worthwhile.
- Gather the main inputs first: current balance, current rate and payment, remaining term.
- Check supporting records such as current statement and early repayment charge quote before relying on a final number.
- Enter one realistic scenario first, using conservative assumptions where the future is uncertain.
- Review the main outputs: new monthly payment, monthly saving, break-even months.
- Run at least one alternative scenario so you can see which input changes the answer most.
- Compare the result with lender illustrations and FCA-regulated mortgage disclosure documents or the relevant contract, bill, statement, or professional document.
- Keep the calculation date and assumptions with your notes so you can revisit the estimate when rates, rules, or circumstances change.
Worked example
Fee break-even check
Input: Monthly saving GBP90 and refinance costs GBP1,800
Calculation: GBP1,800 / GBP90 = 20 months
Result: The refinance breaks even after about 20 months if the saving is achieved.
Short break-even scenario
Input: Switching costs are GBP1,200 and monthly saving is GBP100.
Calculation: GBP1,200 / GBP100 = 12 months.
Result: The switch breaks even after about one year if the saving continues.
Longer-term warning scenario
Input: A borrower lowers payments by refinancing from 15 years remaining to a 25-year term.
Calculation: The calculator compares monthly cost and total interest separately.
Result: The lower payment may improve cash flow but can increase lifetime interest.
When refinancing can help
Refinancing can reduce monthly payments, shorten a term, move from variable to fixed pricing, or release cash. It can also cost more if the new term is longer, fees are high, or the old product has a large early repayment charge.
What to check before relying on the result
A useful Refinance Calculator result starts with the same evidence you would use if you were checking the answer manually. The calculator can organise the arithmetic, but it cannot know whether a payslip is final, a bill is estimated, a quote excludes fees, or a personal circumstance has changed since the last statement.
Before making a decision, compare the calculator result with the source document that controls the real outcome. For this topic, that usually means checking lender illustrations and FCA-regulated mortgage disclosure documents. If there is a difference between the calculator and an official statement, contract, assessment, or professional advice, treat the official document as the stronger source.
- current statement
- Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
- early repayment charge quote
- Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
- new illustration
- Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
- fee schedule
- Use this as supporting evidence for the calculation. If it is out of date, estimated, or based on a different period, the calculator output may look precise while still being wrong for the decision.
Inputs that usually change the answer
The most important input is not always the largest number on the form. Sometimes a date, threshold, percentage, eligibility flag, or timing assumption changes the result more than the headline amount. This is why scenario testing is more useful than a single calculation.
| Input | Why it matters | What to double-check |
|---|---|---|
| current balance | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| current rate and payment | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| remaining term | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| new rate and term | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
| arrangement fees and early repayment charges | It feeds directly into the estimate or changes which rule is applied. | Check the period, units, eligibility, and whether the figure is final or estimated. |
How to interpret the output
The output should be read as a decision aid, not just a number. For Refinance Calculator, the useful question is often what the result means for timing, affordability, eligibility, comparison, or next steps.
- new monthly payment
- Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
- monthly saving
- Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
- break-even months
- Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
- total interest difference
- Use this output alongside the other results rather than in isolation. A monthly amount, percentage, date, or payback figure can look acceptable until fees, timing, evidence, or eligibility conditions are added.
Scenarios worth comparing
A single estimate is a snapshot. A better approach is to save a base case, then adjust one assumption at a time. This shows whether the result is stable or whether a small change in timing, rate, usage, income, or cost creates a very different answer.
| Scenario | Change one assumption | What the comparison shows |
|---|---|---|
| Base case | Use the best current evidence. | Shows the result you would expect if nothing important changes. |
| Conservative case | Use lower income, higher cost, slower growth, or less favourable timing. | Shows whether the decision still works with less optimistic assumptions. |
| Improved case | Use the realistic upside, such as lower cost, better rate, higher usage, or stronger evidence. | Shows the potential benefit without treating it as guaranteed. |
Common mistakes and edge cases
Most errors come from using the right formula with the wrong assumption. Dates can be counted differently, rates can change, official thresholds can move, and real bills or contracts often include conditions that a simple calculator cannot infer automatically.
- A lower payment can cost more if the term is extended.
- Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
- Adding fees to the loan increases interest.
- Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
- Break-even matters if you may move or repay soon.
- Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
- Credit checks and property valuation can affect availability.
- Check this point before using the estimate for a payment, claim, purchase, application, employment decision, or health-related decision.
Next steps after calculating
Once you have a result, write down the key assumptions and compare them with lender illustrations and FCA-regulated mortgage disclosure documents. If the number affects a deadline, tax return, benefit claim, employment issue, medical question, finance agreement, or major purchase, use the calculator as preparation for a more formal check.
For lower-stakes use, the next step may simply be comparing two or three scenarios. For higher-stakes use, the next step should be checking the official guidance, speaking to the relevant organisation, or getting qualified advice before acting.
Important edge cases
- A lower payment can cost more if the term is extended.
- Adding fees to the loan increases interest.
- Break-even matters if you may move or repay soon.
- Credit checks and property valuation can affect availability.
Limitations
This calculator is an estimate and is not mortgage or financial advice. This is general financial information and not mortgage or loan advice. The calculator is designed to support understanding and planning, but it cannot verify documents, predict future rule changes, or account for every exception. Use it as an estimate and check the official source before acting where the result matters.
- It may not include every lender fee or product condition.
- A lower monthly payment can still mean more total interest if the term is extended.
- Eligibility and rates depend on lender underwriting.
- Check lender illustrations and FCA-regulated mortgage disclosure documents for current rules, rates, definitions, and eligibility where relevant.
- Do not rely on a single scenario where income, costs, dates, rates, usage, or health circumstances may change.
- Keep records of the inputs used so that the estimate can be reviewed later.
Frequently asked questions
What is the refinance break-even point?
It is the time needed for monthly savings to recover the fees and charges of switching.
Should I roll fees into the loan?
Rolling fees in can reduce upfront cost but increases the balance and may add interest over time.
Does a lower rate always save money?
No. Fees, term changes, and early repayment charges can outweigh rate savings.
Should I refinance before my fixed rate ends?
Check early repayment charges and product transfer options first. Switching too early can be expensive.
Is APR enough to compare deals?
APR helps, but fees, term, repayment type, and how long you keep the loan also matter.
What if I plan to move soon?
A deal with high upfront fees may not break even before you move or repay.
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