It is difficult to work it out because there are so many variables: but these are my rough calculations: If your gross income is £37k you would save around £1700 by being Ltd. If it is £45k about £2400. The more you earn, the more benefit, because of the higher rate tax you would pay as a sole trader. I would not underestimate the extra pain involved in doing 2 tax returns! unless you particularly enjoy that kind of thing. Generally I would not recommend it unless you are gaining at least £1500 per year. If you are on 60k it would be well worth it.