Open three different credit apps on the same afternoon and you'll get three different numbers for what is supposedly one thing: your creditworthiness. One app might put you at 830 out of 999. Another, checked five minutes later, shows 650 out of 1000. A third, on a completely different scale again, says you're sitting at 580 out of 710. None of these apps is malfunctioning, and none of them is lying to you. They're measuring different things, built from different data, using maths that none of the three agencies will fully disclose.
That gap catches people out precisely when it matters most — a week before a mortgage application, or right after a card gets declined for no obvious reason. Understanding why the numbers diverge, and which one (if any) actually matters to the lender in front of you, is worth ten minutes of reading before you next open one of these apps.
Three agencies, three different files on you
The UK has three credit reference agencies that matter for everyday borrowing: Experian, Equifax and TransUnion — the last of these still remembered by plenty of people under its old name, Callcredit, before the 2018 rebrand. Each one builds its own file on you from data supplied voluntarily by lenders, and no law compels a bank, credit card provider or mobile network to report to all three. A high-street bank might send your mortgage data to Experian and Equifax but skip TransUnion entirely. A buy-now-pay-later firm might report to just one agency, or to none of them at all until fairly recently, when reporting BNPL use became more common practice across the sector. Even something as mundane as a mobile phone contract can end up on one file and not the others, purely because of who the network happens to have a data-sharing agreement with. The result is that your Experian file can contain accounts your Equifax file has never heard of, and the reverse is equally true.
That alone is enough to produce a different score before any scoring formula even gets involved. Two agencies looking at genuinely different sets of accounts will naturally reach different conclusions about the same person.
The scoring scales don't even share a top number
On top of incomplete and inconsistent data, each agency runs its own proprietary model on its own scale, and the three scales aren't remotely comparable. Experian scores out of 999, with anything above 961 rated "excellent". Equifax scores out of 1000, where 811 or higher counts as excellent. TransUnion uses a scale that tops out at 710, where 628 or above is excellent — a scale roughly a third the size of Experian's, covering the same underlying idea. Comparing an Experian 850 to a TransUnion 850 tells you nothing useful, because the TransUnion figure would sit close to the absolute ceiling while the Experian equivalent lands solidly in "good" rather than "excellent" territory.
Treat the headline number as agency-specific and nothing more. Reading three scores as points on one shared ladder is the single most common mistake people make when they check their credit, and it's an easy one to fall into because every app presents its number with the same confident, definitive styling.
Why boosting one score won't automatically fix your mortgage application
Here's the part that trips people up even once they've grasped the scale problem: the number on your phone isn't the number your lender actually sees. Banks and building societies build their own internal risk models, feeding in raw data pulled from one or more of the three agencies, and they weight that data according to their own criteria — often unpublished, sometimes tuned differently for a mortgage than for a credit card from the same bank. A mortgage broker will tell you, correctly, that a 999 Experian score guarantees nothing at the underwriting stage. It's a useful proxy for your general financial behaviour, not a pass mark a lender is contractually bound to honour.
Experian's own Boost feature — which lets you add evidence of regular payments for things like Netflix, Council Tax and mobile contracts to strengthen your file — genuinely can lift your Experian number by a meaningful amount for people with thin credit files. What it can't do is guarantee the same lift shows up in a lender's internal decision, since plenty of lenders pull from Equifax or TransUnion instead, or blend all three. Equifax runs a comparable scheme through its Rental Exchange service, letting on-time rent payments count towards a file for the first time, which matters enormously for renters who've never held a credit card or loan. TransUnion, for its part, tends to weight the most recent 24 months of payment history more heavily than older agencies' models traditionally did, which is why a single missed payment from three years ago can drag an Experian score down for longer than it affects your TransUnion figure.
How to check all three, and what actually costs money
You can see each agency's version of your file without paying anything, provided you know where to look.
- Experian's own app gives you your Experian score and full report free, with no time limit and no trial period to remember to cancel.
- ClearScore pulls Equifax data and is free indefinitely — no card details required at sign-up, which is more than can be said for some of its rivals.
- Credit Karma UK is built on TransUnion data, also free, and tends to update more frequently than the other two — often weekly rather than monthly.
- Checkmyfile shows data from all three agencies (plus Crediva, a newer entrant focused on rental history) side by side in a single report, but it isn't free outright. There's a 30-day trial, and you need to cancel before it rolls into a paid subscription if you only want the one-off comparison.
For everyday monitoring, pick one and stick with it — ClearScore is the sensible default, since it costs nothing indefinitely and updates often enough to flag fraud quickly. Save Checkmyfile for the specific weeks before a mortgage application or a large loan, when seeing all three files at once is genuinely worth the trial sign-up and the reminder to cancel it.
There's also a route that costs nothing and skips the apps entirely: under UK data protection law, you can request your full statutory credit file directly from each agency, free of charge, at any time. It's less polished than the consumer apps — no gamified score, no colourful gauge — but it's the same underlying data a lender's system would draw on, laid out plainly rather than translated into a marketing-friendly number.
What actually moves the number, whichever agency you're looking at
Underneath the differences in scale and coverage, the same handful of factors drive all three scores in roughly the same direction, even if the exact weighting differs.
- Payment history matters more than anything else — a missed payment or default outweighs almost every other factor combined, and it stays visible on your file for six years regardless of which agency reported it.
- Credit utilisation counts heavily too. Keep balances below roughly 25–30% of your available limit across all your cards, not just your total spending for the month.
- Being on the electoral roll at your current address is one of the fastest, cheapest fixes available — agencies use it to confirm your identity, and an unregistered address alone can knock points off an otherwise clean file.
- Financial associations from joint accounts or joint mortgages link your file to another person's, for better or worse. If a former partner's poor credit history is still dragging at your score after you've split finances, file a notice of disassociation with each agency — it's free and usually processed within a few weeks.
- Multiple credit applications in a short window each leave a hard search on your file, and lenders read a cluster of them as a sign of financial stress even when the underlying reason is completely innocent, such as comparing several mortgage deals in the same fortnight.
None of this changes the fact that three agencies will still show you three different numbers next time you check. That's not a bug in the system worth getting worked up about — it's just three separate companies doing three separate, incomplete jobs, and knowing that is worth more than obsessing over which single figure looks best on the day.