It depends on how fluctuating your income is. If the fluctuation is high – for instance, in one month you may make Rs 1 lakh and in the next three months you don’t make anything – you should invest in a liquid or an ultra-short-duration fund and give a standing instruction to move that money over a period of time, say three to six months, into equity funds.If your fluctuating income has a minimum base, make lump-sum investments every month. Be disciplined about them. Whenever you have a surplus, invest it. In effect, this would be like an SIP.