A Stocks and Shares ISA is one of the most powerful wealth-building tools available to UK investors. So if someone invests £500 a month into an ISA for 10 years, how much could they realistically end up with? What index investing could deliverIndices like the FTSE 100 have historically delivered an average total return of around 8% a year. Assuming this continues over the next decade, at that rate, investing £500 a month would build a nest egg worth around £91,473. In terms of money, that means anyone who has been drip feeding £500 each month is now sitting on an eyewatering £221,123!