A credit score can shift when nothing about a person's behaviour has changed. The number is a calculation on a file that is being updated constantly by other parties.
The score is derived, not stored
Credit reference agencies hold a file of accounts, balances, payment histories and searches supplied by lenders.
A score is a model's output when run against that file at a moment in time, so it changes whenever the underlying data changes.
Different agencies hold different data and use different models, which is why a person can see several distinct scores that are all correct on their own terms.
Reporting dates rarely match statement dates
Lenders report balances on their own schedule, usually monthly, and the reported figure is the balance on the reporting day.
Someone who pays a card in full every month can still show a high balance if the report is taken before the payment clears.
Utilisation calculated from that snapshot then moves the score, even though the account has never carried debt from one month to the next.
Account age shifts the picture
Models weigh how long accounts have been open, so closing a long-held account can shorten an average history that took years to build.
Opening a new account has the same effect in reverse, lowering the average and adding a search record at the same time.
Both changes are mechanical rather than judgemental, which is why a score can fall after a step that improves a person's actual position.
Errors and links propagate
Files are matched to people by name and address, and mismatches place another person's account on a file or split one file into two.
Financial associations created by a joint account link two files, and the link persists after the account closes until it is formally removed.
Because these are data problems rather than credit problems, they are corrected through the agency's dispute process rather than through the lender.
Lenders do not use the consumer score
The number shown to a consumer is produced by a general model, while lenders run their own models on the same file plus their own history with the applicant.
A lender also weighs income, existing commitments and its own appetite at that moment, none of which appears in a consumer score.
The consumer number is therefore best read as an indicator of what is on the file, not as a prediction of any particular decision, and anyone facing a specific credit question should take it up with the lender or a qualified adviser.