Monthly overpayment
Use this when you want to add a fixed amount to your mortgage payment each month and see how that changes interest and balance over the next few years.
Mortgage Overpayment Calculator
Mortgage overpayment calculator for regular payments, lump sums and cash comparison
Compare three common choices: adding a monthly overpayment, making a lump-sum payment now, or keeping the same money separate as cash. Check the interest saving and flexibility trade-off before sending extra money to the lender.
Regular overpaymentsLump-sum comparisonCash-access view
Allowance
Check your lender's yearly overpayment allowance and any early repayment charge before sending extra money.
Window
A 2-year or 5-year comparison often matches the period people are actually judging.
Flexibility
Some mortgages support underpayments or payment breaks after prior overpayments, while others do not.
Calculator
Compare the overpayment choice in front of you
Use the monthly tab when you are thinking about a steady extra payment. Use the lump-sum tab if you already have cash available. Use the cash tab when the real choice is between balance reduction and keeping money accessible.
Mortgage Details
£
%
years
years
Use the next 2 years or 5 years if that matches the deal period or budgeting window you are judging.
Monthly Overpayment Plan
£
Check your lender's overpayment allowance and any early repayment charge before committing extra payments.
The calculator keeps the mortgage rate unchanged over the selected window so you can judge the effect of the extra payment itself.
Longer-Term Estimate
The time-saving figure below assumes the same mortgage rate and the same overpayment continue until the balance is cleared. Use it as a guide rather than a promise of what future deals will look like.
Standard Repayment Path
Contractual Monthly Payment
£1,425.29Interest During 2 years
£23,260Balance After 2 years
£239,053With Regular Overpayment
Contractual Monthly Payment
£1,425.29Planned Monthly Outflow
£1,625.29Interest During 2 years
£23,035Balance After 2 years
£234,028Regular Overpayment Summary
Interest Difference Over 2 years
+£225Positive means the overpayment path cuts interest during the selected window.
Balance Difference After 2 years
+£5,025Positive means the overpayment path leaves you owing less at the end of the selected window.
Extra Cash Committed During Window
£4,800This is the extra money you chose to send to the mortgage during the selected window.
Estimated Time Saved If You Kept This Up To Repayment
5 years 2 monthsGuide only. It assumes the same rate and overpayment continue until the mortgage is cleared.
When To Use Each Tab
Three common overpayment decisions
These choices look similar on the surface, but they affect cash flow and flexibility in different ways.
Lump sum now
Use this when you already have money available and want to compare paying it into the mortgage today against keeping it separate.
Keep cash available
Use this when easy access to money matters just as much as reducing the balance. The planner shows the trade-off directly.
Before You Overpay
Checks worth doing before you send extra money
A small detail in your mortgage terms can change the result more than the calculator itself.
Check your allowance and any charge
Many mortgages allow overpayments up to a yearly limit, often 10%, but the exact rule and any early repayment charge depend on the deal you have.
Protect your cash reserve
If the same money is your emergency buffer, short-term moving fund or tax reserve, keeping some or all of it accessible may matter more than the headline interest saving.
Review flexible features
Some mortgages allow payment holidays or underpayments after earlier overpayments. If yours does not, treat extra payments as money you may not be able to draw back later.
Allowance Order
When to use the overpayment planner, ERC calculator and guide together
The safest order depends on whether the payment is clearly inside the allowance, close to the allowance or part of a possible switch.
Inside the allowance
Start with this planner. Compare monthly overpayments, a lump sum and keeping the same cash separate, then read the overpayments guide if you need help with flexibility or emergency-fund trade-offs.
Close to or above the allowance
Run the ERC calculator before treating the interest saving as the answer. A charge on the excess amount can change whether the extra payment still works.
Linked to a deal switch
If the overpayment is happening because a fixed deal is ending or you may leave early, compare the result again in the remortgage planner so product fees and timing are visible.
How To Read The Results
Focus on the comparison window first
For most people, the most useful comparison is what happens over the next few years, not a perfect forecast of the full term.
Interest difference
This shows how much mortgage interest changes over your chosen window. It is useful for judging the immediate effect of the extra payment.
Balance and net debt
Use balance and net debt to compare what you still owe at the end of the window, especially when you are weighing overpayments against keeping cash separate.
Longer-term payoff guide
The payoff-time estimate assumes the same rate and payment pattern continue until the mortgage is cleared. Use it as a guide, not a prediction of future product changes.
Next Tools
Use these tools for the next overpayment trade-off
The overpayment decision often leads straight into another mortgage-management decision.
Overpayments Guide
Check allowance, cash-buffer and flexible-mortgage questions before committing extra money.
ERC Calculator
Estimate the charge if an overpayment would go above the allowance on your current deal.
ERC Guide
Read this if you need to separate allowance rules, exit fees and redemption figures.
Remortgage Planner
Move on here if the overpayment choice is tied to a coming rate switch or product transfer.
Offset Planner
Compare overpaying with an offset structure if keeping cash accessible matters.
Frequently Asked Questions
How much can I overpay without a charge?
Many mortgages allow annual overpayments up to a set percentage limit, often 10%, but the exact allowance and any early repayment charge depend on your own mortgage terms.
Does overpaying always beat saving?
Not always. It depends on your mortgage rate, the savings rate you can actually receive, whether you need easy access to cash and whether your mortgage has charges or flexible features.
Why compare cash as well as mortgage overpayments?
Because the decision is often about flexibility as much as interest. Keeping cash separate may leave you with more accessible money, while overpaying can reduce balance faster.
Can I borrow back overpayments later?
Sometimes, but not always. Some flexible mortgages allow underpayments, payment holidays or access to earlier overpayments, while others do not. Check your lender terms before treating an overpayment as reversible.
Why does the planner focus on a comparison window?
Because most real decisions are tied to the next few years, such as a fixed-rate period, a budgeting horizon or a planned remortgage. Longer-term payoff estimates are useful as guides, but product changes can alter the picture later.