Hi
Its hard for any of us to say, as its based on a number of factors that will be unique to your business, plus your attitude to risk.
Its not about the number of clients neither Im afraid.
Its about worst case scenario and how much it will cost to be put right - the insurance needs to cover ALL of the rectification costs and legals costs of a claim against you. If a client sues for you to fix a mistake it might not be expensive to put the mistake right, it might well be the compensation costs and the legal expenses cover that could 'break the bank'.
So the cover will depend on a variety of factors including the size of the client, the fee size/value, overall turnover, concentration levels (at the moment thats an issue for you as you have two clients who take up say 50% of your time each, which is above the recommended no more than 15% for any one client, but obviously that should shift as you take on more).
Also you need to consider is the compo - any one claim, or in aggregate. Would suggest the any one claim route is better.
What does your prof body stipulate - that needs to be taken into account (as a minimum) so they dont rescind your membership, but otherwise I would suggest the absolute minimum is 2 1/2 x your gross fee income for the year (projected in your case). Although I went for a lot higher than that, even in my first year.
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Joanne
Winner of Bookkeeper of the Year 2015, 2016 & 2017
Thoughts are my own/not to be regarded as official advice,which should be sought from a suitably qualified Accountant.
You should check out answers with reference to the legal position