With ISAs, you pay the income tax upfront and then your investments can grow tax-free inside the ISA wrapper. ISAs can only be funded from your post-tax income, so a limited company cannot just invest in your ISA and benefit from tax savings. From a tax perspective, a pension is a much better option compared to an ISA for limited company directors. However, there has to be a balance. That's because pensions are not accessible until pension age, have a lifetime allowance cap and also attract income tax when money comes out.