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The Wonders of Regular Investment: Dollar Cost Averaging

Updated on February 16, 2015

Regular Investment: Dollar (Pound or Unit) Cost Averaging

"Dollar Cost Averaging" (or DCA) is a grand title given to the mathematical benefits of investing regularly. Feeding your money into the stock-market or bond-market on a monthly basis will reduce the risk of buying on a high day and will in fact ensure that you buy at a price below the average (mean) for the days in question. Human nature encourages people to invest when shares are going up (and already high) and sell when they are going down (and already low) so Dollar Cost Averaging can help to avoid this illogical trait.

DCA will not guarantee you make money, but should help you get a better than average return with reduced risk and in most cases, over long periods will result in a good return way above the returns available from cash or government bonds. This article deals with the pros and cons of DCA and shows how this simple technique works.

Disclaimer: Information in this and other linked articles is unregulated and for general information only and is not intended to be relied upon in making specific investment decisions. Appropriate independent advice should be obtained before making any such decision.

Dollar Cost Averaging

Pound Cost Averaging

Euro Cost Averaging....

Unit Cost Averaging

Mutual Funds

Mutual funds or unit trusts and an ideal investment for dollar-cost averaging strategies.

What is Dollar Cost Averaging and How Does it Work? - Or Pound Cost Averaging in the UK

Dollar Cost Averaging Spread Sheet
Dollar Cost Averaging Spread Sheet

Dollar Cost Averaging is a very simple automatic technique that reduces risk when building an investment portfolio. It is simply the act of regularly investing a fixed amount in an investment. If the price is high you will buy fewer units (or shares) and if the price is low you will buy more of them. It lends itself best to managed fund investment (e.g. mutual funds, unit trusts or OEICs) because it is possible to buy a fraction of a unit and there is usually no dealing charge (just a spread between bid and offer prices) so small regular investments do not cost more than lump sum investments.

The way this strategy works is the amount invested is fixed (i.e. rather than buying a fixed number of units) so more units are purchased on days when the price is low and therefore the average price paid is lower than actual average price over those days. The more volatile the price over the investment period the lower the average price paid relative to the real average.

The Maths: Dollar Cost Averaging

The average price paid per unit or share is actually the harmonic mean rather than the arithmetic mean - The harmonic mean is the reciprocal of the arithmetic mean of the reciprocals.

Return = Price / P(harmonic) -1

where P(harmonic) = harmonic mean = n / (1/X1 + 1/X2 + 1/X3 + .... + 1/Xn)

for a series of n numbers X1, X2, X3, ... Xn

P(harmonic) >= P(arithmetic)

so the return from DCA will generally be more than for the same amount of money invested in a fixed number of shares or units each month.

Pros and Cons of Dollar Cost Averaging

Pros and Cons of DCA

And alternative methods of getting shares at a good price

It all sounds too good to be true. You a are guaranteed to get a price better than the average over the investment period, but in a steadily rising market, you will actually get a price higher than at the start of the period (i.e. you would have been better making a lump sum investment at the beginning) and in a falling market you may have been better wait to the end of the period to invest. DCA does however work very well in volatile markets when the direction is uncertain.

Another problem is fees. If you buy exchange traded funds (ETFs), investment trusts or shares, or any other investment with a fixed trading fee per trade, you will have to pay that fee every month so it may only make sense if the fees are low or the invested sums quite large (although some brokers such as SelfTrade and Interactive Investor) actually reduce the fees for regular investment (just £1.50 per trade) which may make DCA viable even for small sums of money. This is not a problem with unit trusts, mutual funds etc. because there is no trading fee, but the bid-offer spread and annual management fees etc may be quite high.

Most traders and investors will try to time their purchase of shares, stocks, bonds etc. by using techniques such as Technical Analysis (i.e. "Charting") or Fundamental Analysis to determine either when a stock price is likely to move higher or when the price can be considered good value. Both of these methods can (with a lot of practice and effort) give better results, but do require constant monitoring to get the best results. Dollar Cost Average investing requires very little effort.

Dollar Cost Averaging Strategies

Investment Strategies

Dollar Cost Averaging Spread Sheet
Dollar Cost Averaging Spread Sheet

O.K. so if you are a trader or even an active investor this will all sound rather dull, but there are two main stages in a successful trade: buying and selling. Dollar cost averaging may passively get you a good average purchase price, but if you are investing for capital gain you can determine when you want exit the position. e.g. when you have a decent gain compared to the average price paid you can sell and move on to the next "trade". If you are trading unit trusts or mutual funds, however you will never know exactly what price you will get when you sell, because they are priced on a forward basis i.e. you will get the price at the next pricing calculation (typically the following trading day) so there is some uncertainty and you may only want to use this method once gains have significantly exceeded typical daily volatility.

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    • KathyZ1 profile image

      KathyZ1 3 years ago

      Interesting lens. Thanks for your sharing.

    • javr profile image

      javr 6 years ago from British Columbia, Canada

      Very helpful information. This lens has been blessed by a Squid Angel.

    • profile image

      anonymous 6 years ago

      You are solid Andy. Thanks for your advice that you give. I like that graph!

    • SandyMertens profile image

      Sandy Mertens 6 years ago from Frozen Tundra

      Good information as always.