What a credit score is actually measuring

A credit score is not a measure of wealth, income, or virtue. It is a prediction of one narrow thing: how likely you are to fall 90 days behind on a payment in the next two years. Every quirk of how it is calculated follows from that.

It explains why a millionaire who has never borrowed can score worse than someone on a modest salary with a decade of paid-on-time cards. The score has no opinion about your finances. It has only ever been asked one question.

What goes into it

FICO publishes the weightings, and they are not evenly distributed:

• Payment history — 35%. Do you pay on time. The largest single factor by some distance.
• Amounts owed — 30%. Mostly credit utilisation: your balances against your limits.
• Length of credit history — 15%. The age of your accounts, including the average.
• New credit — 10%. Recent applications and hard inquiries.
• Credit mix — 10%. Whether you have handled different kinds of borrowing.

Two categories account for 65% of the outcome, and both are behavioural rather than structural. Pay on time, keep balances low relative to limits, and you have done almost everything that moves the number.

The one that surprises people: utilisation

Utilisation is your reported balance divided by your limit. Crucially, it is usually measured on your statement date, not after you pay. Someone who charges $4,500 on a $5,000 limit and clears it in full every month — paying zero interest, behaving impeccably — can still report 90% utilisation and be marked down for it.

The fix is mechanical: pay part of the balance before the statement closes, ask for a limit increase, or spread spending across cards. None of that changes your finances at all. It changes the snapshot.

This is also why closing an unused card can lower your score. You remove its limit from the denominator, so the same spending suddenly looks like heavier borrowing.

What barely matters

Carrying a balance to “build credit”. This is a myth that costs real money. Paying in full builds history exactly as well and costs nothing in interest.

Checking your own score. A soft inquiry. It has never affected anything.

Income, savings, and net worth. Not in the score at all. Lenders consider them separately.

A single hard inquiry. Typically a small, temporary effect. Rate shopping for a mortgage or auto loan within a short window is generally treated as one inquiry, so comparing lenders does not compound the damage.

What it is worth in money

The score is not a game — it is priced into every loan you take. Take the same $320,000 mortgage at two plausible rates for different credit tiers:

• Stronger credit, 6.25% — $1,970 a month, $389,306 of total interest.
• Weaker credit, 7.75% — $2,293 a month, $505,307 of total interest.

A difference of $322 every month and $116,001 across the loan — for the same house, the same borrower, a different number on a file.

The short version

Pay everything on time, without exception — it is a third of the score and the only factor where a single mistake lingers for years. Keep reported balances well under your limits. Leave old accounts open. Apply for new credit sparingly, and cluster rate shopping into a tight window.

Then largely forget about it. The behaviours that produce a good score are the same ones that produce good finances, which is the one genuinely reassuring thing about the system.

Weightings are FICO's published general model; VantageScore and lender-specific models differ. The mortgage rates above are illustrative tiers, not current market quotes.