Warren Buffett advice that could put you on the path to ISA millionaire status

ISA millionaire status is a goal that many investors aspire to. And with a sensible long-term investment strategy in place, it's a goal that is definitely achievable now that annual ISA allowances are larger than they were in the past. With that in mind, today I'm sharing some investment advice from the greatest investor of all time, Warren Buffett. Could these tips help you achieve your goal of building a seven-figure ISA portfolio?

Keep it simple

"Your goal as an investor should simply be to purchase, at a rational price, a part interest in an easily-understandable business whose earnings are virtually certain to be materially higher five, ten and twenty years from now."

This is a fantastic quote from Buffett and a good place to start when choosing companies to invest in. Long-term investing really doesn't need to be that complicated. Buy into companies that are almost certain to be bigger in a decade than they are today, and you can't go too far wrong.

Treat stocks like businesses

"I view the stocks that Berkshire owns as interests in businesses, not as ticker symbols to be bought or sold based on their 'chart' patterns, the 'target' prices of analysts or the opinions of media pundits."

One of the keys to Buffett's success has been his long-term, 'business-owner' approach to investing. You see, unlike many investors, Buffett is largely unconcerned with short-term price movements. Instead, he invests as if he is a part-owner in the business and gives the company he has invested in plenty of time to grow and prosper. In his words, his favourite holding period is "forever."

It can be hard to invest like this at times, especially when we are faced with constant news and opinions about the stocks we own. The key is to ignore short-term noise and focus on the long view.

Stick to what you understand

"There's a whole bunch of things I don't know a thing about -- I just stay away from those. So, I stay within what I call my circle of competence."

Another important thing to note about Buffett's investment strategy is that he only dives into businesses he understands. A look at his holdings reveals name such as American Express and Coca-Cola - companies that have quite simple business models. He advises investors to draw a circle around the businesses they understand, and then eliminate those that fail to qualify on the basis of value, good management and limited exposure to hard times.

Go against the herd

"I will tell you how to become rich. Close the doors. Be fearful when others are greedy. Be greedy when others are fearful."

Lastly, Buffett understands that sometimes the best investing opportunities arise during moments of market turbulence. When there's panic in the air and high-quality businesses are being marked down in price, it can be a good time to add to your portfolio. With the FTSE 100 down over 10% in the last two months, is that time now?

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