July 3, 2026
9 Min Read
If you have started looking at houses, you have probably seen the phrase "mortgage in principle" turn up on every estate agent's checklist, usually with no explanation of what it actually is or why they want it before they will even talk to you about an offer. It is one of the first real hurdles a first-time buyer hits, and it arrives at the exact moment everything already feels complicated.
The good news is that a mortgage in principle is one of the simpler parts of buying a home. It is a quick, early step that tells you roughly what you can borrow and shows sellers you are serious. It is not the mortgage itself, and getting one does not lock you into anything. This guide explains what a mortgage in principle is, how to get one, how long it lasts, what it does to your credit file, and the mistakes that catch buyers out, so you can walk into the process knowing exactly what you are holding.
What is a mortgage in principle?
A mortgage in principle (MIP) is a written statement from a lender indicating how much they may be willing to lend you, based on the basic financial information you give them. It is also called an agreement in principle (AIP) or a decision in principle (DIP). The three terms mean the same thing.
It is an estimate, not a promise. The lender looks at your income, your outgoings, your deposit, and usually a credit check, and produces a figure that says, in effect, "on what you have told us, we would consider lending around this much." It gives you a realistic budget before you start making offers, and it gives an estate agent confidence that you can afford the homes you are viewing.
The key thing to understand is what a mortgage in principle is not. It is not a formal mortgage offer. The lender has not yet verified your documents, valued a property, or run a full application. So while the figure is useful for planning, it can still change once the real checks happen. Think of it as the lender's first look at you, not their final answer. If you want to understand how it fits into the wider buying journey, our mortgage and protection service walks you through every stage from first enquiry to completion.
How to get a mortgage in principle
Getting a mortgage in principle is usually quick, often same-day. You can apply directly with a lender or, more commonly for first-time buyers, through a mortgage broker who can match you to the right lender before you apply. The lender or broker will ask for a set of basic details and run an initial assessment.
What you will need to provide
You do not need a pile of paperwork for this stage, but you do need accurate figures. Lenders typically ask for your name, date of birth and address history, your annual income (including any bonus, overtime or self-employed profit), your regular outgoings and existing debts, the size of your deposit, and the rough value of the property you want to buy. The more accurate these are, the more reliable the figure you get back.
The credit check
Most lenders run a credit check as part of producing a mortgage in principle. This is where a broker earns their keep, because some lenders use a soft check (invisible to other lenders, no impact on your score) while others use a hard check (which leaves a footprint on your file). Applying for several mortgages in principle in a short space with hard checks can dent your score, so it is worth knowing which type a lender uses before you apply. A broker will steer you toward soft-check lenders first and only run a hard check when you are ready to commit.
Once submitted, you usually get a decision within minutes to a few hours, along with a certificate or reference number you can show to estate agents. If you are buying with a partner, both of you are assessed together, since the lender looks at your combined income and combined commitments.
How long does a mortgage in principle last?
A mortgage in principle is not open-ended. Most last between 30 and 90 days, with 60 to 90 days being the most common. The lender sets the window because your financial circumstances, and their lending criteria, can change over time.
This matters more than buyers expect, because finding the right house often takes longer than the certificate lasts. It is common to get a mortgage in principle, view homes for a couple of months, and find your certificate has lapsed just as you are ready to offer. When that happens, you do not start from scratch. You renew it, which is usually straightforward and, with many lenders, can be done without a fresh hard credit check.
The practical advice is simple: do not rush to get a mortgage in principle the moment you start daydreaming about moving. Get it when you are genuinely ready to view and offer, so the clock is working for you, not against you. If your circumstances change during the window, a new job, a change in income, a missed payment, tell your broker, because it can affect the figure when you move to a full application.
Why estate agents ask for a mortgage in principle
Estate agents almost always ask to see a mortgage in principle before they will put your offer to the seller, and there is a straightforward reason. The agent's job is to find the seller a buyer who can actually complete. A mortgage in principle is the quickest piece of evidence that you are a real buyer with funding behind you, not someone who likes the house but cannot get the money.
In a competitive market, this can be the difference between your offer being taken seriously and being ignored. If two buyers offer the same amount and one has a mortgage in principle ready while the other says they "need to sort the mortgage out," the seller will usually go with the one who can move. It signals that the chain is less likely to collapse on the funding side.
It also protects you. Going through the mortgage in principle process forces you to find out your real budget before you fall in love with a house you cannot afford. Plenty of first-time buyers set their heart on a property, only to discover at the full application stage that the borrowing was never there. Doing it early turns a vague hope into a firm number. Buying often runs alongside a property purchase that needs legal work too, and our conveyancing team can run in step with your mortgage so the two sides do not hold each other up.
Common mortgage in principle mistakes to avoid
A mortgage in principle is simple, but there are a handful of errors that cause real problems later. Knowing them in advance saves time, stress and sometimes the house itself.
Giving rounded or optimistic figures. The certificate is only as accurate as the numbers you put in. Overstate your income or forget a loan, and the figure you get is fiction. When the full application checks your payslips and statements, the borrowing can shrink, and that is a horrible moment to discover mid-purchase. Put in real numbers from the start.
Applying to lots of lenders with hard checks. Several hard credit searches in a short period can lower your score and make lenders nervous. This is exactly why going through a broker helps, since they narrow the field before any hard check is run.
Treating it as a guarantee. A mortgage in principle is an indication, not an offer. The full application can still be declined if the property does not meet criteria, the documents do not match what you declared, or your circumstances change. Keep your finances steady between the mortgage in principle and completion, no new car finance, no big credit card spending, no job changes if you can help it.
Leaving it too late, or doing it too early. Too early and it expires before you offer. Too late and you lose the house to a buyer who was ready. The sweet spot is getting it just as you start serious viewing. A broker can time this with you. Many first-time buyers also overlook the protection side of buying a home, which our protection advisers can look at alongside the mortgage so your home is covered from day one. For the government's own plain-English overview of the home-buying process, the GOV.UK buying and selling a home guide is a useful companion.
Frequently asked questions
How long does a mortgage in principle last?
A mortgage in principle usually lasts between 30 and 90 days, depending on the lender, with 60 to 90 days being most common. If it expires before your offer is accepted, it can normally be renewed, often without a fresh credit check.
Does a mortgage in principle affect my credit score?
It depends on the lender. Some run a soft check, which other lenders cannot see and which does not affect your score. Others run a hard check, which leaves a footprint. A broker can point you to soft-check lenders before you apply, so you avoid unnecessary marks on your file.
Is a mortgage in principle a guarantee I will get the mortgage?
No. It is an indication based on the information you provide, not a binding offer. The lender still has to verify your income, value the property, and complete a full application before issuing a formal mortgage offer.
Can I be refused a mortgage after getting a mortgage in principle?
Yes. An application can still be declined at the full stage if your circumstances change, your documents do not match what you declared, or the property does not meet the lender's criteria. This is why getting an accurate mortgage in principle, with honest figures, matters from the start.
Do I need a mortgage in principle to view houses?
You can view without one, but most estate agents will ask to see a mortgage in principle before they take an offer seriously. Having one shows you are a credible buyer who can move quickly, which can matter a great deal in a competitive chain.
A mortgage in principle is one of the easiest wins in the whole home-buying process. It costs nothing, it usually takes minutes, and it turns a vague hope into a real budget while showing sellers you mean business. The trick is to treat it for what it is: an early indication, not a finished deal. Get your figures right, time it so it does not expire before you offer, watch how the credit checks are run, and keep your finances steady between the mortgage in principle and completion. Do those four things and the rest of the mortgage process gets a lot calmer. If you would rather not work out which lenders use soft checks and which will lend the most on your numbers, that is exactly the job a broker does, and it is where having one team handle the mortgage, the protection and the legal side together saves you chasing four people at once.
