How Credit Scores Work: The Five Factors That Move Them
What goes into a FICO score, how much each factor is worth, how fast each one moves, and which common beliefs about building credit are simply wrong.
How do credit scores work? A credit score is a statistical prediction of one thing: how likely you are to fall 90 days behind on a payment in the next two years. Five inputs feed it, and two of them are roughly two-thirds of the answer. Payment history is about 35%, credit utilisation about 30%, length of history 15%, credit mix 10% and new credit 10%.
A credit score is therefore a prediction, not a grade. It answers exactly one question for a lender: how likely is this person to fall 90 days behind on a payment in the next two years? Everything in the formula exists to serve that prediction, which is why some things that feel responsible do not help, and some things that feel harmless do damage.
How do credit scores work: the five factors
The widely used FICO model weights them roughly like this:
| Factor | Approximate weight | How fast it moves |
|---|---|---|
| Payment history | 35% | Slowly. Damage fades over years. |
| Amounts owed (utilisation) | 30% | Immediately, within one cycle. |
| Length of credit history | 15% | Only with time. |
| Credit mix | 10% | Slowly, and barely worth managing. |
| New credit | 10% | Recovers within 12 months. |
The first two are about 65% of the score. If you are trying to move a number, that is where the leverage is. The rest is worth understanding so you do not accidentally damage it, but it is not where you spend effort.
Why does one late payment hurt so much?
Whether you paid on time, on every account, going back seven years.
A single payment 30 days late can drop a good score substantially: the drop is larger the higher your score was, because there is more to lose. It then stays on your report for seven years, fading in influence but never fully invisible until it drops off.
What counts as late is worth being precise about. Missing your due date by a few days is a fee and possibly a lost promotional APR, but it is not reported to the bureaus. Reporting starts at 30 days past due. That gap is a genuine grace period: if you realise on day 12 that you missed a payment, paying immediately means it never reaches your credit report.
Automate the minimum, not the full balance
Set autopay for the minimum payment on every card and loan, then pay the full statement balance manually. If a manual payment fails or you forget, autopay catches it and the account never goes 30 days late. Automating the full balance risks an overdraft in a bad month, which creates a different problem.
Also on this factor: collections, charge-offs, repossessions, foreclosures and bankruptcies. If any of them is wrong, disputing it is free and takes about 30 days. A paid collection is better than an unpaid one, and newer scoring models ignore paid collections entirely, but older models that many lenders still use do not.
What is credit utilisation and how fast does it move?
The percentage of your available revolving credit you are currently using. If you have $20,000 in total card limits and $4,000 in reported balances, you are at 20%.
Two things make this factor unusually useful:
It has no memory. Utilisation is calculated on what is reported right now. Last year's 90% does not linger. Pay the balances down and the score responds on the next reporting cycle, typically within 30 days.
It is measured per-card and overall. One maxed card can hurt even when your total utilisation is low. Spreading a balance across two cards can score better than concentrating it on one.
Below 30% is the usual advice. Below 10% is where scores actually optimise. Zero across every card is very slightly worse than a small reported balance, because the model wants to see the account being used, but the difference is a few points and not worth engineering.
The statement date trick
Issuers report your statement balance, not the balance after you pay. Someone who spends $3,000 a month on a $5,000-limit card and pays in full still gets 60% utilisation reported. Making a payment a few days before the statement closes drops the reported balance, and the score, without changing what you spend or what you pay in interest, which is nothing.
Length of credit history
The age of your oldest account, your newest, and the average of all of them. There is no shortcut. The only lever is not destroying what you have.
This is why closing an old card is usually a mistake. Closed accounts in good standing stay on your report for around ten years, so the age effect is delayed rather than immediate, but the lost credit limit hits your utilisation the same day.
Credit mix
The model likes to see you handle both revolving credit (cards) and instalment credit (car loans, mortgages, student loans). It is 10%, and you should never take on debt you do not need to improve it. If you have only cards, a future car loan or mortgage will add the mix naturally.
New credit
Each hard inquiry from an actual application costs a handful of points and stops counting after twelve months, though it stays visible for two years.
The important exception: rate shopping for a mortgage, car loan or student loan is treated as a single inquiry when the applications fall inside a short window, typically 14 to 45 days depending on the model. Shopping several lenders for one loan does not compound the damage. Applying for four credit cards in a month does.
Opening a new account also lowers your average account age, which is a small second hit.
The CFPB explanation of credit scores is the neutral reference if you want to verify any of this, and the FTC covers your dispute rights.
What do people get wrong about credit scores?
"Carrying a balance builds credit." It does not. This is the single most expensive misconception in consumer finance. Your statement balance is reported whether or not you pay it off, so paying in full builds identical history at zero interest cost.
"Checking my score lowers it." Soft inquiries (your own checks, pre-approval offers, account reviews) have no effect at all.
"I have no debt, so I must have great credit." Someone with no credit accounts at all may be unscorable. The model needs history to predict from.
"Income affects my score." It does not appear in the formula. Lenders consider it separately when deciding whether to approve you, but it is not part of the score.
"There is one credit score." There are dozens. Different FICO versions, VantageScore, industry-specific auto and card variants, and three bureaus each holding slightly different data. The score your card app shows you may not be the one your mortgage lender pulls.
How do you fix a low credit score?
Highest impact first
- Bring every account current. Nothing else matters while something is past due.
- Pay revolving balances below 10% of each card's limit, and below 10% overall.
- Ask for credit limit increases on existing cards. A higher limit lowers utilisation without you doing anything else.
- Pull all three reports free at AnnualCreditReport.com and dispute anything wrong. Errors are common and disputes are free.
- Stop applying for new credit for six months.
- Leave old cards open. Put one small recurring charge on each so the issuer does not close it for inactivity.
- If you are starting from nothing, a secured card or being added as an authorised user on someone else's well-managed old account both build history.
What a score is worth in dollars
This is the part that makes it concrete. On a 30-year $350,000 mortgage, the spread between a 760+ borrower and a 640 borrower is often more than a percentage point of interest. Over the life of the loan that difference runs well into six figures.
On a car loan the gap is smaller in absolute terms but proportionally larger, and on insurance premiums (many states permit credit-based insurance scores) the effect shows up every year, quietly, forever.
That is the practical answer to how do credit scores work in the terms that matter, and the honest case for caring about it. Not because the number is a report card, but because two people with identical incomes and identical houses can pay wildly different amounts for the same things, and the only difference is a three-digit prediction about which of them misses a payment.
Frequently asked
What is a good credit score?
On the common 300-850 FICO scale, 670 and above is generally considered good, 740 and above very good, and 800 and above exceptional. The practical thresholds that change what you are offered tend to sit around 620, 660, 720 and 760, above 760 you are usually getting the best pricing available, and further points buy little.
How long does it take to improve a credit score?
It depends on the factor. Paying down balances can move a score within one billing cycle, typically 30 days. Late payments fade gradually and drop off after seven years. Hard inquiries stop affecting the score after twelve months. Building age takes exactly as long as it takes.
Does checking my credit score lower it?
No. Checking your own score or report is a soft inquiry and has no effect. Only a hard inquiry from an actual credit application counts, and each one costs a few points at most for up to twelve months.
How can I raise my credit score quickly?
Pay revolving balances down below 10% of each card limit, and request credit limit increases on the cards you keep. Utilisation recalculates every statement cycle with no memory of previous months, so it is the only factor that can move a score materially within 30 days. Everything else, including late payments and account age, improves only with time.
How many credit scores do I have?
Dozens. There are multiple FICO model versions plus VantageScore, industry-specific auto and bankcard variants, and three bureaus each holding slightly different data. The score in your banking app is often not the one a mortgage lender pulls, which is why small differences between sources are normal and not worth chasing.
Do I need to carry a balance to build credit?
No, and this is the most expensive myth in personal finance. Card issuers report your statement balance whether or not you carry it into the next month. Paying the statement balance in full every month builds exactly the same history and costs nothing in interest.
Sources
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