A decision in principle is not a mortgage offer

These are listed in the order worth acting on, which with mortgage decisions in principle is not the order they are usually presented in.

What the document actually is

A decision in principle records that, on the information supplied and a credit check, a lender would consider lending a stated amount. The information at that stage is usually self-declared, so income, deposit and outgoings have been stated rather than proven. Its commercial purpose is to let sellers and agents filter serious buyers, which is a real benefit and a different thing from a commitment.

Names differ by market, and terms such as agreement in principle or pre-qualification describe broadly the same limited undertaking. Read the document itself rather than the covering message, because the conditions are usually stated plainly inside it.

The search it leaves behind

Some lenders run a soft search for a decision in principle while others run a hard search that later lenders can see. Collecting several hard-searched decisions in a short period produces a cluster that can itself weigh against the eventual application. Ask which type of search will be used before you proceed, since the answer is not consistent across lenders or even across products.

In practice, where you are simply testing the market, a soft-searched route or a broker who knows lender criteria avoids unnecessary footprints. Once you are committed to a purchase, one hard search with the lender you intend to use is the efficient path.

What full underwriting adds

The full application verifies income with documents or transaction data, examines bank statements and reviews the deposit and its source. Identity, fraud and anti-money-laundering checks run properly at this stage, and unexplained large deposits routinely cause delays.

For most people, the property is valued, and a valuation below the agreed price can reduce the amount the lender will advance regardless of your finances. Legal work may surface issues with the title, lease or construction that make the lender unwilling to lend on that specific property. Any of these can change or end the application even though the decision in principle was issued without difficulty.

Why it can be withdrawn

A decision in principle is conditional by construction, so it lapses if the facts turn out differently from the ones declared. Changing job, taking new credit, or a change in the lender own criteria between the indication and the application can all remove it. These documents carry an expiry date, commonly measured in months, after which the whole assessment has to be redone.

Lenders also reprice and retighten across their whole book, which can withdraw an indication for reasons that have nothing to do with you. Treating the indication as money already secured is the mistake that leads to committing to a purchase you cannot complete.

The things that most often derail it

Taking any new credit between the indication and completion is the classic error, because it changes commitments and adds a fresh search. Gifted deposits without a clear paper trail cause repeated delays, since the lender must evidence where the money came from.

A change from employed to self-employed status, even to better-paid work, can remove eligibility until a trading record exists. Missed payments during the process, including on accounts you consider trivial, can trigger a re-check that changes the outcome. The safest posture between indication and completion is to change nothing at all about your financial arrangements.

Using it sensibly

Obtain one when you are genuinely ready to offer, not while browsing, so that its validity period covers the period you need. Keep the supporting documents assembled from the outset, because speed at full application often decides whether a chain survives.

Put simply, be honest in the declared figures, since the verification stage will find the difference and an inconsistency reads as a risk signal. Ask what conditions attach to the indication and what would cause it to be reviewed, and keep the written answer. Mortgage decisions carry long consequences and vary enormously by country, so regulated advice is the appropriate route for anything specific.

Everything above, in order of what to do first

1. What the document actually is. A decision in principle records that, on the information supplied and a credit check, a lender would consider lending a stated amount.
2. The search it leaves behind. Some lenders run a soft search for a decision in principle while others run a hard search that later lenders can see.
3. What full underwriting adds. The full application verifies income with documents or transaction data, examines bank statements and reviews the deposit and its source.
4. Why it can be withdrawn. A decision in principle is conditional by construction, so it lapses if the facts turn out differently from the ones declared.
5. The things that most often derail it. Taking any new credit between the indication and completion is the classic error, because it changes commitments and adds a fresh search.
6. Using it sensibly. Obtain one when you are genuinely ready to offer, not while browsing, so that its validity period covers the period you need.

The takeaway

Get one when you are ready to offer, change nothing afterwards, and remember that the lender has verified none of it yet.

Small and repeatable beats ambitious and abandoned, almost every time.