Image source: Getty Images I would like to receive emails from you about product information and offers from The Fool and its business partners. Each of these emails will provide a link to unsubscribe from future emails. More information about how The Fool collects, stores, and handles personal data is available in its Privacy Statement. Simply click below to discover how you can take advantage of this. The FTSE 100 has risen from 1,000 points to its current price level of around 6,600 points since it was established in January 1984. As such, an investor who bought and held a diverse range of companies from the index could realistically have doubled their investment in large-cap stocks.Of course, there is no guarantee that the index will rise at all in future. It may spend the next decade at a lower price than where it trades today. However, its track record, low valuations across the index and the potential for compounding suggest otherwise. It means an investment made today could realistically double over the long run in a bull market.5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…A 100% return from the FTSE 100The FTSE 100 has recorded annual capital growth of around 5% over the last 37 years. But its total returns are significantly higher when dividends are added. In fact, their reinvestment has been a large part of the total returns of UK shares in recent decades. They have turned mid-single-digit annual returns into high-single digit compounded returns.As mentioned, there is no guarantee that a similar level of return will be achieved in future. The future never mirrors the past, of course. However, the past performance of the index suggests that it has the capacity to produce new record highs after the 2020 stock market crash. It has always been able to achieve this goal in the past – even after its very worst crashes and bear markets.For illustration purposes, I will assume it does follow a similar return profile in future as it has done in the past. This means an investment made today could realistically produce 100% returns within a decade. As such, this could be significantly ahead of the returns of other mainstream assets over the same time period that have lower yields or higher prices than many large-cap shares.Managing a portfolio of UK sharesClearly, the FTSE 100 is far riskier than other popular assets such as cash and bonds. Therefore, it is imperative to diversify across a broad range of companies to reduce company-specific risk. So, too, is ensuring that only amounts of capital that are not required for everyday spending are invested in shares. Otherwise, they may need to be sold to cover expenses during what could prove to be a challenging economic period.Of course, the stock market’s past returns have not been linear. They have been hugely volatile at times – as the last year has shown. More ups and downs are likely in the coming years, as the economic uncertainty currently present plays out. However, history suggests that buying a broad range of large-cap shares and holding them for the long run has been a successful means of generating relatively attractive returns. This theme may continue after what has been a tough period for the stock market. Peter Stephens | Friday, 29th January, 2021 Get the full details on this £5 stock now – while your report is free. FREE REPORT: Why this £5 stock could be set to surge Enter Your Email Address Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. See all posts by Peter Stephens Our 6 ‘Best Buys Now’ Shares FTSE 100 watch: could UK shares double my money during the new bull market? Are you on the lookout for UK growth stocks?If so, get this FREE no-strings report now.While it’s available: you’ll discover what we think is a top growth stock for the decade ahead.And the performance of this company really is stunning.In 2019, it returned £150million to shareholders through buybacks and dividends.We believe its financial position is about as solid as anything we’ve seen.Since 2016, annual revenues increased 31%In March 2020, one of its senior directors LOADED UP on 25,000 shares – a position worth £90,259Operating cash flow is up 47%. (Even its operating margins are rising every year!)Quite simply, we believe it’s a fantastic Foolish growth pick.What’s more, it deserves your attention today.So please don’t wait another moment.