EXPATRIATES should use their stint in Hong Kong's low-tax environment to build a healthy nest egg before returning home, investment professionals advise. But the territory's high cost of living means money slips through the fingers unless a conscious effort is made to save. 'Just invest. Like Nike, just do it,' BT Fund Managers vice-president Grant Forster said. 'Because it's the discipline of compound interest and regular investment that will get you home at the end of the day.' Speaking at an Australian Chamber of Commerce investment seminar last week, he said a young person who socked away seven annual instalments of $2,000 starting at age 19 would, assuming a yearly return of 10 per cent, end up with a retirement pool of $944,641 - without ever having to save another cent past the age of 25. Meanwhile, a person who waited until age 26 to start saving but then set aside 40 annual instalments of $2,000 would retire with only marginally more money - $973,704 - than the first person. 'You've just got to do it and keep investing and not try to time things because . . . it's too difficult,' Mr Forster said. Another colleague from down under, Jardine Fleming Unit Trusts director Tony McDonald, concurred. He said it was futile to try to time the market because the big trading days were random and unpredictable. 'It's time, not timing,' he said. Tracing the Hang Seng Index for the past 20 years, Mr McDonald said the combined results of all 7,300 trading days worked out to an annualised return of 18.5 per cent. To demonstrate the arbitrary power of big one-day gains, he stripped out the top five days and the rate of return slipped to 15.8 per cent. Minus the 50 biggest-gain days, the annual return sank to 2.6 per cent. Because these blockbuster days were impossible to predict, Mr McDonald urged savers to make their investments using dollar-cost averaging - that is, invest a set amount each month, no matter what the market does. This approach guaranteed a below-average share cost, he said. For example, if you decide to invest $100 each month, this will get you 100 mutual-fund units when the unit price is $1 and 143 when the price is 70 cents. Taking the two months together, the average unit price works out to 85 cents. But your average cost is only 82 cents because you automatically bought more units when the price was low. Highlighting the importance of a long-term perspective, Mr Forster said that although the Australian All Ordinaries had posted losses over one and five-year periods, it had never done so over 10 and 15-year stretches. 'The younger you are, the more shares you can have [as a portion of your portfolio],' he said.