How much professional indemnity insurance costs depends on what you do far more than on how big you are. Two businesses of identical turnover in different professions can be quoted figures that differ by a multiple, which is why no average across professions is worth quoting.
The activity sets the band
Insurers rate professional indemnity by the claims record of the work. Low risk advisory and administrative activities price cheaply. Design, construction related work, financial advice and surveying price higher. Describing the activity precisely gets you the right band; describing it vaguely gets you a cautious one.
Income and limit set the position in it
Fee income is a proxy for the volume of work exposed, and the limit is what you are buying. Raising the limit costs less than proportionally, because the insurer's expected loss sits in the smaller claims, which is why a higher limit is usually better value than buyers assume.
What you can do about it
Declare the activity accurately, tidy your contracts, keep engagement letters, and buy the limit your clients actually require. Those four move a quote more than shopping the same risk to three brokers does.
Questions people ask about how much is professional indemnity insurance
Is there an average figure?
None worth quoting. The activity alone moves the premium by multiples across professions.
Does doubling the limit double the price?
No, it costs less than proportionally, which makes a higher limit unusually good value.
What is the fastest way to a lower quote?
Describe the activity precisely and have engagement letters and liability caps in place. Both change the underwriting.