The Big 4 premium, band by band
Every UK company that files audited accounts says what it paid its auditor. Put those fees side by side, size for size, and the question of whether the four largest firms cost more has a number on it: yes, about three times, but only from about £10m of revenue.
What the filed fees say
The United Kingdom is unusual in one useful way: the audit fee is a line in the notes to every set of audited accounts, and Companies House publishes the accounts. auditor.ltd reads that line from every filing it can, cleans it, and groups the fees by the company’s revenue. As of 10 September 2026 that is 31,677 fees, with a national median of £15,000 across every size and sector.
Size explains most of the spread. A company with under £1m of revenue pays a median £12,500; one with £10–25m pays £15,750; one with £100m or more pays £28,730. The interesting question is what is left once size is held still, and that is where the auditor’s name comes in.
Three tiers, one revenue band at a time
The site sorts firms into three tiers: the Big 4 (Deloitte, EY, KPMG and PwC), the challenger networks (the forty or so national and regional groups such as BDO, Forvis Mazars, Azets, Saffery and Moore), and everyone else, the independent firms. Within each revenue band, the median fee of each tier is computed separately, so a Big 4 fee is only ever compared with fees from companies of the same size.
For a company with £10–25m of revenue, the band with the most fees on file, the medians are:
| Auditor tier | Median fee | Fees on file |
|---|---|---|
| Big 4 | £45,000 | 23 |
| Challenger | £18,900 | 2,528 |
| Independent | £14,725 | 5,278 |
That is a Big 4 fee 3.1 times an independent firm’s and 2.4 times a challenger’s. One band up, at £25–50m, the pattern holds: £52,960 at the Big 4 against £23,000 and £18,000.
Where the premium disappears
Below £5m of revenue there is no Big 4 premium to speak of. Companies with under £1m of revenue paid a median £15,086 to a Big 4 firm and £15,690 to a challenger; at £1–5m the figures are £12,750 and £13,975. Independent firms are cheaper in both bands, at £11,228 and £10,314, but the gap between the Big 4 and the challengers is gone.
Part of the reason is visible in who those small companies are. The Big 4’s clients with a fee on file are small: Deloitte’s median client on file has £302,000 of revenue, KPMG’s £60,000, and Deloitte’s most frequent client sectors on file are building-project development, business support services, holding companies and head offices. Entities like these sit inside larger groups, and the fee attached to each one is small. A Big 4 audit of a stand-alone £2m trading business is not what those figures describe.
How small the Big 4 sample is
Read the counts as carefully as the medians. In the £10–25m band there are 23 Big 4 fees on file against 5,278 from independent firms; at £25–50m there are 20. In the bands between, and above £50m, there are fewer than twenty and the site publishes no figure, because a median over a handful of fees describes those companies rather than the market. The premium is real in the two bands where it can be measured; how it behaves above £50m, where the site holds fewer than twenty Big 4 fees in any band, is not something these filings settle.
What the four firms look like on their own
Across every band, on the clients with a fee on file:
| Firm | Mandates | Fees on file | Median fee |
|---|---|---|---|
| Deloitte LLP | 191 | 123 | £17,067 |
| Ernst & Young LLP | 127 | 75 | £25,530 |
| KPMG LLP | 99 | 38 | £15,310 |
| PricewaterhouseCoopers LLP | 66 | 33 | £36,625 |
Year on year, on clients with two consecutive fees on file, Deloitte’s median fee rose 10.5% (25 pairs) and EY’s 4.2% (29 pairs), against a market median of +5.0% across 14,618 companies. KPMG and PwC have too few pairs on file for a figure.
What to do with this
If your company has £10m or more of revenue and a Big 4 auditor, the filed fees of companies your size say the market rate at a challenger or independent firm is between a third and a half of what you pay. Whether that trade is worth making depends on what the audit is for: a lender or an acquirer who expects a Big 4 name is a reason to stay, and a company that is not listed, not regulated and not for sale has fewer of those reasons. The benchmark puts your own filed fee against companies your size in seconds, and the alternatives pages list the firms that audit companies like yours, with their median fee.
Questions this article answers
How much more does a Big 4 audit cost in the UK?
On the audit fees filed with Companies House, a company with £10–25m of revenue pays a median £45,000 to a Big 4 firm, £18,900 to a challenger firm and £14,725 to an independent firm: about three times an independent firm's fee and 2.4 times a challenger's. At £25–50m the medians are £52,960, £23,000 and £18,000.
Is there a Big 4 premium for small companies?
Not in the filed fees. Companies with under £5m of revenue paid the Big 4 and the challenger firms about the same (£15,086 against £15,690 under £1m; £12,750 against £13,975 at £1–5m). The Big 4's small clients on file are holding companies, head offices and other entities inside larger groups, with a median revenue in the hundreds of thousands of pounds.
Which of the Big 4 is the most expensive?
Across every size of client with a fee on file, PwC's median fee is £36,625, EY's £25,530, Deloitte's £17,067 and KPMG's £15,310. The four have different mixes of clients on file, so the medians say as much about who they audit as about their rates.
