The government sets the investment limits and the current allowance for the tax year which runs from 6 April to 5 April is £9,000 or £750 per month. This amount can be split between a stocks & shares JISA and a cash JISA, providing the overall limit is not exceeded in the tax year (6 April to 5 April). The minimum in the Sheffield Mutual Investment JISA is £10 per month or a single lump sum of £100.