A mortgage is where a credit score stops being an abstraction. Lenders price risk in bands, and on a loan this size the distance between bands is measured in tens of thousands of dollars over the term.
For scale: the US 30-year fixed averaged 6.67% for the week ending 13 August 2026. On a $400,000 loan, a quarter-point difference in the rate you’re offered is roughly $65 a month, about $23,000 across thirty years. That’s what this ninety days is worth.
Only two things move fast
Of the five scoring categories, exactly two respond inside a three-month window.
Credit utilisation. 30% of a FICO score, and the reported figure is a snapshot rather than a history. Change it and the change appears at the next report.
Errors. Not a category, a correction, and potentially the largest single gain available if something wrong is sitting on your file.
Payment history is the biggest category at 35% and it heals slowly. Length of history is 15% and accrues at one month per month. Neither is a lever in this window; both are reasons to have started earlier.
Days 1–30: find out what lenders will see
Pull all three reports. The CFPB is explicit that you don’t have one score: different bureaus hold different data, and a mortgage lender may pull a bureau you never check. An error on one file is invisible until it costs you.
Dispute anything wrong immediately, in writing, with evidence. Investigations take time, so this is the step that has to happen first rather than last.
Note every statement closing date. You’ll need them in month two.
Pay down the highest-ratio cards. Target the cards using the largest share of their own limit, not the biggest dollar balances — utilisation is measured per card as well as overall.
Days 31–60: work the timing
Most issuers report your statement balance. This means someone who pays in full every month can still report high utilisation, simply because the payment lands after the statement date.
Pay before the statement closes. Same money, lower reported number. It’s free and it’s the single most underused move available.
Ask for limit increases on existing cards, but only where the issuer will do it without a hard inquiry. Ask that question explicitly before requesting. A higher limit lowers utilisation without you paying anything down.
Days 61–90: freeze everything
This is the part people get wrong, usually with good intentions.
Do not open any new account. Not a card, not a car loan, not store finance for the sofa you’re planning for the new house. Each one is a hard inquiry plus a zero-age account, and underwriters look closely at recent credit activity.
Do not close any account. Closing removes available credit and pushes utilisation up. It feels tidy; it works against you.
Do not make large purchases on credit. A furniture or appliance spree between pre-approval and completion has sunk real applications, because lenders re-check before closing.
Do not change jobs if avoidable. Not a scoring issue, an underwriting one. Income stability is assessed separately and a recent move complicates it.
What lenders look at beyond the number
The score opens the door; the file gets read.
Recent activity. A flurry of applications in the last six months invites questions even if the score survived them.
Payment history in detail. A single late payment two years ago is a very different thing from three in the past year, and underwriters see the pattern rather than just the total.
Debt-to-income ratio. Separate from the score entirely, and often the binding constraint. Paying down a card helps here as well as with utilisation, which is why it’s the highest-value action in this whole window.
If your score is genuinely low
Ninety days of utilisation work will not transform a file carrying recent missed payments or a default. That’s worth knowing before you spend three months hoping.
In that situation the better plan is usually to delay the application, spend six to twelve months building a clean record, and buy at a materially better rate. Or talk to a broker about what’s realistically available now. What actually increases a score covers the longer programme, and how long it genuinely takes sets expectations honestly.
The last check before you apply
Pull your reports one final time and confirm the improvements have landed. Then stop touching anything until completion.
Your score decides which band you land in. It’s the market that decides where those bands sit, and that part is entirely out of your hands.