It is one of the curiosities of personal finance that marketing for individual savings accounts (ISAs) is concentrated at the end of the tax year. The March weekend papers are full of ISA ads and supplements, but by May any trace of ISAs has melted away (excuse the pun).
Logically, the time to invest in ISAs is at the start of the tax year. The sooner you invest, the more time you have to benefit from the tax advantages ISAs have to offer. There is no need to wait for the dying months of the tax year to determine how much you can invest. Even if you cannot make the maximum £10,680 investment now, an early start with some contribution still has financial logic. Bear in mind that up to half of the £10,680 limit can be in cash, and it could make sense to move cash deposits from tax-bearing accounts (up to £5,340) early in the tax year. This would allow you to stop paying income tax on the switched amount.
The value of your investment and the income from it can go down as well as up and you may not get back the full amount you invested. Investing in shares should be regarded as a long-term investment and should fit in with your overall attitude to risk and financial circumstances. The value of tax reliefs depends on your individual circumstances. Tax laws can change.