Most letters are written to expire in 60 to 90 days, because the credit report and the pay stubs behind them go stale before the loan would, and renewing one is a refresh of documents plus a new credit pull rather than a new application.
The date on the letter is not a rule anybody made about pre-approvals. It is a lender working backwards from the shelf life of the paperwork the approval was built on, and picking a date short enough that everything is still current if you write an offer on the last day. Knowing which document expires first tells you what a renewal will cost you in effort, which is almost nothing.
Why 60 to 90 days and not a year
The binding constraint is the age of the file. The agencies require credit documents to be no more than four months old on the note date, and that outside limit covers the credit report, the income documents and the asset statements together. A lender writing a 90-day letter is leaving itself room: if you go under contract on day 90, the file still has weeks of life before signing.
Inside that, individual documents have shorter lives. Pay stubs are normally wanted within about 30 days of use, bank statements are the two most recent, and employment is verified again close to funding regardless of what the file already holds. A credit score itself does not expire, but the report it came from does, and scores move.
Renewing is a refresh, not a restart
In practice a renewal is an email: the last two pay stubs, the newest bank statements, and confirmation that nothing has changed about the job, the debts or the down payment. The lender re-runs the file and issues a letter with a new date. It usually takes hours, not days, which is why letting one lapse while you are still looking is a mild nuisance rather than a problem.
The part people ask about is the credit pull. A renewal normally involves a new hard inquiry, and mortgage inquiries are treated gently by the scoring models: inquiries for the same purpose inside a window are counted as one, and that window runs from 14 to 45 days depending on which model version a lender is using. A second pull from the same lender two months later is a separate inquiry, and one mortgage inquiry is a small effect on a score compared with the credit-card balance sitting on the same report.
What the letter is not
A pre-approval is not a commitment to lend. It is a conditional statement based on documents supplied before a property existed, and the loan is still underwritten with an appraisal, a title report and refreshed credit attached. Sellers read it as evidence a lender has actually looked at the file, which is why it beats a pre-qualification, but no letter obliges anybody to fund.
The rate is a separate thing again. A pre-approval quotes a rate as an assumption for the payment math; a rate lock is what fixes it, and a lock is normally taken once there is a property and a contract. Nothing about a 90-day letter holds a price for 90 days.
The number on it is a ceiling, not a target
The amount on a pre-approval is the largest loan the lender's ratios allow with the debts and income in the file. It is calculated on principal, interest, property tax, insurance, mortgage insurance and any HOA dues against gross monthly income, before income tax, before childcare, before whatever you actually spend. A payment at the top of the letter is a payment that qualifies, which is a different claim from one that fits.
There is also a housekeeping use for the number. Many buyers ask their lender for a second letter written at the offer price rather than the maximum, so the seller is not handed the ceiling during a negotiation. The lender can issue both from the same approval; it is the same file with a different figure typed on it.
Questions people ask
What happens if my mortgage pre-approval expires?
Nothing happens to your credit or your file. The letter simply stops being usable with an offer, and the lender reissues it once you send current pay stubs and statements. Plan on a day if the lender has to re-verify employment or wait on a statement cycle.
Does renewing a pre-approval hurt your credit?
Only slightly, and less than most people expect. A renewal usually means a new hard inquiry, mortgage inquiries within a 14 to 45 day window count as one depending on the scoring model, and a single mortgage inquiry is a minor factor next to balances and payment history.
Is a pre-qualification the same as a pre-approval?
No. A pre-qualification is an estimate from numbers you stated, often with no documents and sometimes with no credit pull. A pre-approval means the lender pulled credit, read the documents and ran the file. In a competitive offer the difference is visible to the listing agent.