What is a mortgage and how does it work?

What Is a Mortgage and How Does It Work?

A mortgage is a long-term loan used to buy a property.

In the UK, a lender gives you money towards the purchase of a home, and the property acts as security for the debt.

You normally put in a deposit, borrow the rest, and repay the mortgage over time through monthly payments.

That sounds simple, but a mortgage is not just “money for a house”.

It is a legal and financial agreement that affects what you can buy, what your monthly budget looks like, how much interest you may pay, and how flexible you are later if you want to move, remortgage, overpay or change product.

If you are a first-time buyer, the simplest way to think about a mortgage is this:

A mortgage is the bridge between the home you want and the cash you have today.

The strength of that bridge depends on your deposit, income, credit profile, lender criteria, property value and the type of mortgage deal you choose.

👉 Check what mortgage options may suit your situation.

What does a mortgage mean?

A mortgage is a loan secured against a property.

That means the lender has a legal charge over the home until the mortgage is repaid.

If you keep up with the mortgage payments, the loan reduces over time if you are on a repayment mortgage.

If you do not keep up with the payments, the lender can take action, and your home may ultimately be at risk.

That is why mortgage affordability matters so much.

A mortgage is not only about getting approved.

It is about making sure the payments are realistic for your income, lifestyle and future plans.

How does a mortgage work in practice?

A residential mortgage usually works like this:

1. You save or receive a deposit. 2. You apply to a lender for the rest of the purchase price. 3. The lender checks your income, outgoings and credit history. 4. The lender checks whether the property is acceptable security. 5. If approved, the mortgage helps fund the purchase. 6. You repay the mortgage through monthly payments.

The mortgage runs for an agreed term, such as 25, 30 or 35 years.

During that time, you may change mortgage deals several times.

You may start on a fixed rate, move to another fixed rate later, remortgage, switch lender, overpay, move home or change term.

Mortgage term vs mortgage deal

One of the biggest mortgage misunderstandings is the difference between the mortgage term and the mortgage deal.

They are not the same thing.

Your mortgage term is the full length of time over which the mortgage is scheduled to be repaid.

For example, this could be 25 or 30 years.

Your mortgage deal is the interest-rate arrangement for a shorter period.

For example, you may have:

• a 2-year fixed rate
• a 5-year fixed rate
• a tracker deal
• a discounted variable deal

When the deal ends, the mortgage itself does not end.

The rate deal ends.

If you do nothing, you may move onto the lender’s follow-on rate or standard variable rate.

For more detail, read what happens at the end of a fixed-rate mortgage?

What is a mortgage deposit?

Your deposit is your contribution to the purchase price.

If you buy a property for £250,000 and put down a £25,000 deposit, you need a £225,000 mortgage.

The deposit matters because it affects:

• how much you need to borrow
• your loan-to-value
• the mortgage rates available
• lender choice
• monthly payments
• approval chances
• the lender’s risk

A bigger deposit can improve your options, but it does not remove affordability checks.

You still need to show the lender that the mortgage is affordable.

For more detail, read how much deposit do you really need?

What is loan-to-value?

Loan-to-value, often called LTV, is the percentage of the property value that you are borrowing.

For example:

LTV matters because lenders often price mortgages in bands.

A lower LTV can sometimes give access to better rates.

A higher LTV can mean fewer product options or stricter criteria.

This is why mortgage planning is not only about asking, “How much can I borrow?”

It is also about asking, “What LTV band will I be in?”

For more detail, read what is loan-to-value LTV and why it matters.

What is a repayment mortgage?

A repayment mortgage is the most common type of residential mortgage.

With a repayment mortgage, each monthly payment usually includes:

• interest charged by the lender
• part repayment of the original amount borrowed

Over time, the mortgage balance should reduce.

If you make all payments as agreed, the mortgage should be fully repaid by the end of the mortgage term.

For most people buying a home to live in, a repayment mortgage is the simplest and most straightforward structure.

What is an interest-only mortgage?

With an interest-only mortgage, your monthly payments usually cover only the interest.

The original mortgage balance does not reduce through normal monthly payments.

You still need a plan to repay the capital at the end of the mortgage term.

That repayment plan might involve savings, investments, sale of property or another accepted strategy, depending on lender criteria.

Interest-only can exist in residential lending, but it is more restricted and not suitable for everyone.

The lower monthly payment can look attractive, but the debt still needs to be repaid later.

Repayment vs interest-only: simple comparison

Repayment mortgage: - pays interest and capital - balance gradually reduces - clearer route to owning the home outright - monthly payment is usually higher than interest-only Interest-only mortgage: - pays only interest each month - balance does not reduce automatically - needs a separate repayment strategy - monthly payment may be lower, but capital remains owed

For most first-time buyers, repayment is usually easier to understand.

Interest-only needs careful advice and a credible repayment plan.

What is a fixed-rate mortgage?

A fixed-rate mortgage keeps your interest rate the same for a set period.

Common fixed-rate periods include:

• 2 years
• 3 years
• 5 years
• 10 years

The main advantage is certainty.

Your monthly payment is usually predictable during the fixed-rate period.

This can help with budgeting.

The trade-off is flexibility.

Fixed-rate deals often come with early repayment charges if you leave, repay or switch during the fixed period.

For more detail, read fixed vs variable mortgages: which is better right now?

What is a variable mortgage?

A variable mortgage has an interest rate that can change.

This means your monthly payment can rise or fall.

Variable mortgages can include:

• tracker mortgages
• standard variable rates
• discount variable mortgages

A variable mortgage may appeal if you want flexibility or think rates may fall.

But it can be risky if your budget is tight because payments can increase.

What is a tracker mortgage?

A tracker mortgage usually follows a specific rate, often the Bank of England base rate, plus a lender margin.

For example:

Bank Rate + 1.00%

If the tracked rate rises, your mortgage rate usually rises.

If the tracked rate falls, your mortgage rate may fall too.

Tracker mortgages can be more transparent than some other variable rates, but they still involve payment uncertainty.

For more detail, read what is a tracker mortgage?

What is a standard variable rate?

A standard variable rate, or SVR, is the lender’s own variable rate.

You may move onto SVR when your initial deal ends if you do not arrange a new product.

SVRs are often higher than new fixed, tracker or product-transfer deals.

They can also change at the lender’s discretion.

Being on SVR temporarily may make sense in some situations, such as if you are about to move home.

But drifting onto SVR by accident can be expensive.

For more detail, read how remortgaging can save you money.

How do mortgage payments work?

Your monthly mortgage payment depends on several factors.

These include:

• amount borrowed
• interest rate
• mortgage term
• repayment type
• product fees
• overpayments
• rate changes
• whether the mortgage is repayment or interest-only

On a repayment mortgage, each monthly payment includes interest and capital repayment.

At the start of the mortgage, more of the payment may go towards interest.

As the balance reduces, more of the payment can go towards repaying the debt.

The exact split depends on the mortgage structure and interest rate.

How do lenders decide whether to approve a mortgage?

Mortgage lenders assess risk and affordability.

They usually want to know:

• how much you earn
• how stable your income is
• what debts you have
• what your regular outgoings are
• whether you have dependants
• whether your credit history is acceptable
• where your deposit came from
• whether the property is suitable security
• whether the mortgage looks affordable now
• whether it could still be affordable if rates rise

This is why a mortgage is never only about salary.

Income matters, but so do commitments, credit history, deposit, property type and lender criteria.

For more detail, read how mortgage lenders assess affordability.

What is mortgage affordability?

Mortgage affordability is the lender’s assessment of whether the mortgage is realistic for your financial position.

The lender may look at:

• basic salary
• bonus
• commission
• overtime
• self-employed income
• contractor income
• student loan deductions
• childcare
• car finance
• credit cards
• personal loans
• dependants
• household costs
• mortgage term
• interest rates
• future rate risk

A mortgage can be affordable for one household and unrealistic for another, even if the property price is the same.

For more detail, read how much can I borrow for a mortgage in the UK?

What is a mortgage stress test?

A mortgage stress test is part of the lender’s affordability thinking.

It considers whether the mortgage would still appear affordable if payments increased or circumstances became less favourable.

This can matter if:

• rates rise
• your initial deal ends
• your income is variable
• the lender uses a higher assessment rate
• you are borrowing near the maximum
• you have other debts
• affordability is tight

A stress test can reduce how much you are able to borrow.

For more detail, read how mortgage stress tests actually work.

What is a Mortgage in Principle?

A Mortgage in Principle is an early indication from a lender of what it may be prepared to lend.

It is also called:

• Agreement in Principle
• Decision in Principle
• AIP
• DIP
• MIP

It can help you understand your rough borrowing position before making offers.

It can also help estate agents take you more seriously.

But it is not a full mortgage offer.

A full application still depends on documents, affordability, credit checks, underwriting and property valuation.

For more detail, read what is a Mortgage in Principle?

What documents do you need for a mortgage?

The documents needed depend on your situation.

Common examples include:

• payslips
• bank statements
• proof of ID
• proof of address
• proof of deposit
• employment contract
• P60
• self-employed accounts
• tax calculations
• tax year overviews
• gifted deposit letter
• credit explanations
• existing mortgage statement

The aim is to prove your income, deposit and affordability clearly.

For more detail, read can you get a mortgage without proof of income?

What does the property valuation do?

A lender usually needs to check that the property is acceptable security for the mortgage.

This may involve a valuation.

The lender’s valuation is mainly for the lender, not for you.

It helps the lender assess whether the property is worth enough to support the mortgage.

It is not the same as a detailed survey for your own protection.

For more detail, read what is a mortgage valuation and why it matters?

What costs come with a mortgage?

The monthly mortgage payment is only part of the cost.

You may also need to budget for:

• product fees
• arrangement fees
• valuation fees
• survey costs
• legal fees
• broker fees
• stamp duty where applicable
• buildings insurance
• contents insurance
• moving costs
• service charges
• ground rent where applicable
• maintenance and repairs
• early repayment charges
• exit fees

Home ownership affordability is not the same as mortgage affordability alone.

A mortgage may pass the lender’s checks but still feel uncomfortable if the wider cost of owning the property is ignored.

For more detail, read what fees are involved in getting a mortgage?

What is an early repayment charge?

An early repayment charge, or ERC, is a fee that may apply if you leave, switch or repay a mortgage deal before the agreed period ends.

ERCs are common on fixed-rate deals and some tracker or discount products.

They can matter if you:

• want to move home
• want to remortgage early
• plan to make large overpayments
• may sell soon
• expect your circumstances to change

A low rate may not be the best choice if it locks you into a product that does not fit your plans.

For more detail, read can you move house without paying early repayment charges?.

Can you overpay a mortgage?

Many mortgages allow some overpayments.

Overpaying can reduce the mortgage balance and may reduce total interest over time.

But overpayment rules vary.

You should check:

• how much you can overpay
• whether limits apply
• whether ERCs apply
• whether overpayments reduce the term or monthly payment
• whether keeping savings is more important
• whether other debts should be repaid first

Overpaying can be useful, but it should fit your wider finances.

For more detail, read mortgage overpayments: are they worth it?

What happens after your first mortgage deal ends?

When your first mortgage deal ends, you usually have options.

You may:

• take a new deal with your current lender
• remortgage to a new lender
• move onto SVR
• choose a fixed rate
• choose a tracker
• adjust the term
• borrow more if suitable
• make overpayments
• review your protection needs

Doing nothing may be expensive if you move onto SVR by accident.

This is why mortgage planning should continue after completion.

For more detail, read what is remortgaging and how does it work?

Why mortgage choice matters beyond approval

Many buyers start with the question:

Can I get approved?

That matters, but it is not the only question.

A better question is:

Which mortgage structure gives me the best balance of affordability, resilience, flexibility and long-term cost?

That shift matters.

A cheap-looking deal with restrictive early repayment charges may not suit someone planning to move.

A long mortgage term may reduce monthly payments but increase total interest.

A variable rate may look appealing, but it can be uncomfortable if payments rise.

The right mortgage should fit your life, not just the lender’s calculator.

Common mortgage myths

“The cheapest rate is always the best mortgage.”

Not always.

Fees, flexibility, incentives, tie-ins, product length and future plans all matter.

“If I can borrow the maximum, I should.”

Not necessarily.

The maximum mortgage may be possible without being comfortable.

“Once my fixed rate ends, the mortgage ends.”

No.

The deal period ends, not the mortgage term.

“The lender valuation protects me from buying a bad property.”

Not really.

The lender’s valuation is mainly for the lender. A buyer survey is separate.

“A bigger deposit always means I can borrow more.”

Not always.

A bigger deposit can improve LTV and product choice, but affordability still matters.

“A Mortgage in Principle guarantees approval.”

No.

It is an early indication, not a full mortgage offer.

A practical way to think about a mortgage

The strongest mortgage decision is not the one that stretches you the furthest.

It is the one that still works when life is a bit untidy.

A sensible mortgage should leave room for:

• utility price changes
• repairs and maintenance
• childcare changes
• commuting costs
• insurance
• savings
• income changes
• interest-rate changes
• remortgage planning
• moving plans
• emergency costs

This is a more trustworthy approach than chasing maximum borrowing.

Sustainable home ownership is the real win.

How a broker can help

You do not have to use a broker, but a broker can help you compare lenders and mortgage structures.

A broker may help with:

• affordability checks
• lender criteria
• rate comparison
• fixed vs variable decisions
• deposit and LTV planning
• first-time buyer options
• self-employed income
• contractor income
• bad credit
• complex income
• remortgage planning
• product transfers
• documentation
• avoiding unsuitable applications

A broker cannot guarantee approval.

But they can help you understand the options before you commit.

For more detail, read how getting a mortgage without a broker works.

Related guides

If you are learning how mortgages work, these guides may also help:

• If you are buying for the first time, read first-time buyer mortgages explained.
• If you want to understand borrowing power, read how much can I borrow for a mortgage in the UK?
• If you want an early lender indication, read what is a Mortgage in Principle?
• If you want to understand deposit and LTV, read what is loan-to-value LTV and why it matters.
• If you are comparing rates, read fixed vs variable mortgages: which is better right now?
• If you want to understand affordability, read how mortgage lenders assess affordability.
• If you are using online estimates, read are online mortgage calculators accurate?
• If your deal is ending, read what is remortgaging and how does it work?

These guides work together because a mortgage involves deposit, LTV, affordability, credit history, interest rates, deal periods, lender criteria and long-term ownership costs.

FAQs about mortgages

What is a mortgage?

A mortgage is a loan used to buy property. The loan is secured against the property, which means the lender has rights over the home if the mortgage is not repaid.

How does a mortgage work?

You usually put down a deposit, borrow the rest from a lender, buy the property, and repay the mortgage through monthly payments over an agreed term.

What is the difference between a mortgage term and a mortgage deal?

The mortgage term is the full length of the mortgage. The deal is the shorter interest-rate period, such as a 2-year or 5-year fixed rate.

What happens when a mortgage deal ends?

You may move onto the lender’s standard variable rate unless you arrange a new deal or remortgage.

What is a repayment mortgage?

A repayment mortgage means your monthly payments cover interest and part of the original loan, so the balance reduces over time.

What is an interest-only mortgage?

An interest-only mortgage means you pay the interest each month, but the original loan still needs to be repaid at the end of the term.

What is LTV?

LTV stands for loan-to-value. It is the percentage of the property value that you are borrowing.

Do I need a deposit for a mortgage?

Usually, yes. The deposit reduces the amount you need to borrow and affects your LTV.

Is the cheapest mortgage rate always best?

Not always. Fees, early repayment charges, flexibility, product length and your future plans also matter.

Should I borrow the maximum I can?

Not necessarily. The right mortgage should be affordable in real life, not just possible on paper.

Bottom line

A mortgage is a long-term loan used to buy a property, but it is more than a simple borrowing arrangement.

It affects your deposit, monthly budget, interest costs, ownership plans, flexibility and future remortgage options.

The most important parts to understand are:

• how much you are borrowing
• how much deposit you have
• your loan-to-value
• whether the mortgage is repayment or interest-only
• whether the rate is fixed, tracker or variable
• how long the deal lasts
• how long the mortgage term lasts
• what the lender checks before approving you
• what happens when the deal ends
• what the true monthly and long-term costs are

The strongest mortgage is not always the one that lets you borrow the most.

It is the one that fits your income, property, plans and budget properly.

👉 Check your mortgage options today — free, quick and no obligation.