What Is a Mortgage in Principle? Slough Broker Guide

You have not even made an offer yet, and already you are worried. What if you look at homes in Slough you cannot actually afford. What if you waste weeks falling for a house that was always out of reach.

A mortgage in principle sorts this out early, so you are not guessing.

Here is the short answer. A mortgage in principle is a written estimate from a lender of how much they might let you borrow, based on a quick check of your finances. It is not a guarantee, but it gives you a realistic budget before you start looking, and it usually takes less than a day to get.

What is a mortgage in principle?

A mortgage in principle is sometimes called an agreement in principle, a decision in principle, a mortgage promise, or a lending certificate. They all mean the same thing.

It is a document from a lender saying roughly how much they would be willing to lend you, based on limited information about your income and outgoings. It is not a formal offer, and it does not commit either side to anything.

Do you need a mortgage in principle?

It is not a legal requirement. But in practice, most estate agents will ask for one before they book you in for viewings, especially in a competitive area. Some will not take your offer seriously without one. Slough’s market moves quickly in places, particularly for flats near the town centre and homes close to the Elizabeth line stations, so having one ready can make a real difference to how fast you can act. In Scotland, you may not get a viewing at all unless you already have one in place.

If you are early in your search and just want a rough idea of your budget, it is still worth getting one. It costs nothing and takes very little time.

What information do you need?

You will usually need:

• Your name, date of birth, and National Insurance number
• Your address history for the last three years
• Details of your income, including salary, bonuses, benefits, or pensions
• Your monthly outgoings, including credit cards, loans, and childcare costs
• The size of your deposit and the price of the property, if you have one in mind

If you are self employed, most lenders will want two to three years of accounts or tax calculations rather than payslips.

Not sure how much deposit you will need before you start this process? Our guide on how much deposit you need for a mortgage breaks this down.

How long does it take to get one?

Many lenders can give you a decision within an hour if you apply online and have everything ready. In most cases, you should have an answer within 24 hours. It can take a little longer if your situation is more complex, such as being self employed or having irregular income.

How long does it last, and can it change?

A mortgage in principle usually lasts between 30 and 90 days, depending on the lender. There is no single fixed number across the market, so always check with whoever issued yours.

If it expires before you have found a property, you can usually renew it. Worth knowing though, the amount on offer can change even if nothing about your own situation has. Interest rates and property values shift over time, and lenders adjust what they are willing to offer as a result.

Does it affect your credit score?

This depends on the lender. Some only run a soft check, which does not show on your file and has no impact on your score. Others run a hard check, which does leave a mark, though a single check on its own should not damage your score.

The thing to watch is applying too many times in a short period. Several hard checks close together can make lenders think you have been turned down elsewhere, even if that is not what happened. If you are not sure which type of check a lender uses, it is worth asking before you apply.

Can you get more than one?

Yes. You are not tied to one lender, and it is common to compare offers from a few before deciding. Just be mindful of the credit check point above if you are applying directly with several lenders yourself.

This is one of the places working with a broker instead of going straight to your bank genuinely saves you time and protects your credit file, since they can compare lenders without you needing to submit several separate applications.

Mortgage in principle vs mortgage offer

	Mortgage in principle	Mortgage offer
What it is	An estimate of what you could borrow	A confirmed offer for a specific property
When you get it	Before or during house hunting	After your offer is accepted and you apply in full
Based on	Basic income and outgoings, a quick credit check	Full affordability check, property valuation, hard credit check
Guaranteed?	No	Yes, provided nothing changes before completion

What could stop you getting a mortgage after this?

Having a mortgage in principle does not guarantee a final offer. A few things can still get in the way:

• The property itself. Some lenders will not lend on flats above a certain height, homes without a working kitchen or bathroom, or certain non standard buildings.
• A lower valuation. If the property is valued below the price you agreed, your final offer may come in lower than your mortgage in principle.
• New information at full application. A hard credit check or closer look at your finances can sometimes turn up something a quick check did not.

None of this means you should worry unnecessarily. It just means the mortgage in principle is a strong early guide, not the final word.

Is a mortgage in principle legally binding?

No. Either you or the lender can walk away at this stage without any penalty. It also does not fix the property price. Technically, a seller could still raise their asking price later, since nothing is legally binding until contracts are exchanged.

Have you had credit problems before? You may still be able to get one

A poor credit history in the past does not automatically rule you out. It may mean a bit more explanation is needed, or that only certain lenders are a good fit for your situation. This is exactly where speaking to a broker early can save you from applying with a lender who was always going to say no.

How a broker helps at this stage

Getting a mortgage in principle yourself is simple enough. Where a broker genuinely helps is afterwards:

• Comparing lenders properly, rather than guessing which one suits your situation
• Avoiding a mortgage in principle that later gets undercut by a lower final offer
• Managing multiple applications without racking up unnecessary credit checks
• Explaining any past credit issues to the right lender in the right way

Brokers are usually paid a fee by the lender once a mortgage completes, not by you directly, so getting advice at this stage does not typically cost you anything extra. Read more about why using a broker instead of going straight to your bank tends to be faster and less stressful.

What happens after you get a mortgage in principle?

Once you have one, you can start house hunting with a realistic budget in mind. When you find a property and have an offer accepted, your broker will help you move to a full mortgage application.

Curious how long that next stage takes? Our guide on how long a mortgage application takes through a broker walks through it step by step.

Getting a mortgage in principle for a property in Slough

The mortgage in principle process itself is identical wherever you buy in the UK, but a few things are worth knowing if you are house hunting locally.

• New build flats near the town centre and Elizabeth line stations often move fast, so estate agents in these areas are especially likely to ask for a mortgage in principle before booking a viewing.
• Older properties in the surrounding villages, such as Wexham, Datchet or Iver, can occasionally fall under non standard construction. It is worth flagging this to your broker before you apply, so your mortgage in principle is checked against a lender who is comfortable with the property type.
• Local knowledge helps at the credit check stage too. A broker who regularly places applications with lenders active in the Slough and Berkshire area is more likely to know which ones run a soft check versus a hard check, so you are not caught out.

None of this changes how long a mortgage in principle takes or how long it lasts. It just means a local broker can often steer you toward the right lender the first time, rather than after a rejection.

What to do next

Frequently Asked Question.