Dollar cost averaging

Dollar cost averaging (DCA) is a technique of buying a fixed dollar amount of a particular investment on a regular schedule, regardless of the share price. More shares are purchased when prices are low, and fewer shares are bought when prices are high. Dollar cost averaging is considered an alternative to investing a lump sum, although the term is often used to describe similar investment concepts such as periodic automatic investment (almost universally utilized by individual investors to fund retirement accounts out of earned income) or "reverse dollar cost averaging" which pertains to periodic automatic withdrawals made during retirement. Value averaging closely resembles dollar cost averaging but differs in that the investor selects a target growth rate or amount on his or her asset base or portfolio each period, and then adjusts the next period's contribution according to the relative gain or shortfall made on the original asset base.

Dollar cost averaging versus lump sum
When you are ready to invest money, a common question is whether you should invest it as a lump sum or Dollar Cost Average (DCA) by splitting your investment across several payments. The answer depends on your psychology.

In most cases, you are moving your money from cash (or the equivalent, a low-yielding money market) to some mix of  stocks and  bonds. The expected value of both stocks and bonds are higher than cash. However, their volatility is higher as well. The risk is that just after making your investment, the market could crash, causing you to feel bad that you invested when you did.

Of course, according to Bogleheads Investment Philosophy, you should only be investing in the first place into a diversified asset allocation. Also, you should only be holding volatile funds like stocks and bonds if your investing horizon is long enough to ride out their volatility.

For a completely rational investor, lump sum investing will always produce a higher expected return, because it immediately moves your funds from asset classes with lower expected returns to ones with higher expected returns. Note that higher expected returns do not guarantee that your actual returns will be higher. According to an investopedia article, studies indicate that lump sum investing has produced higher returns 66% of the time.

Some investors have the goal, not of maximizing their expected returns, but of minimizing their potential regret. For those investors, dollar cost averaging is superior because it reduces the chances of investing just prior to a market drop. If you instead decide to invest 1/6th of the money each month for 6 months, you will reduce the chance of buying just before a crash. Instead, as the price fluctuates each month, you will buy more shares when the price is low and less when it is high.

Many new investors are more interested in minimizing their potential regret, and it's important that an ill-timed market drop not scare them off from investing in the future. Many experienced investors are more interested in maximizing their expected returns. You can also decide to split the difference, where you invest half immediately and the other half over 6 or so months.

Costs
Most no-load mutual funds allow small, regular investments with no fees. However, most investors pay a commission to purchase a load-fund or an ETF. Depending on the size of the commission and the investment, DCAing into a load-fund or an ETF could be far more expensive than purchasing as a lump sum. For ETFs, the bid/ask spread is the same between DCA and lump sum.

Automatic investment
Most investors make regular contributions through their 401(k) plans or by having a set amount auto-deducted from their bank account into an IRA or taxable account. When this money is automatically invested, it has the same benefit of dollar cost averaging that you buy more shares when prices are low and less when they are high. However, this form of investing is not dollar cost averaging. It is called periodic investing. The difference is that periodic investing is maximizing expected return, because you are investing the money as soon as you have it. DCA applies when you have the money to invest, but delay doing so.

Switching to a more conservative portfolio
Some investors who are new to a Bogleheads Investment Philosophy may find their portfolios contain too much equity. Even worse, some investors have a large portion of their net worth held in a single stock, such as through an employee purchase plan. They generally want to sell some of their equities and buy bonds. In these cases where an investor wants to move from high risk and volatility assets to lower risk and volatility assets, a lump sum transaction makes more sense than DCA. That's because lump sum both immediately moves to the expected return and volatility the investor wants, while also minimizing potential regret.

Reverse dollar cost averaging
Investors who regularly add to their investment portfolios with periodic investing purchase more shares when prices are low and less shares when prices are high. Author Henry K. Hebeler points out that investors  periodically distributing retirement income from their portfolios experience the reverse action, redeeming more shares when prices are low and less shares when prices are high. Hebeler terms this process, "reverse dollar cost averaging" with results that should, on average, reduce expected returns. Examining rolling 20 year investment periods from 1927 to 1995 for a portfolio consisting of 50% large cap stocks (S&P 500); 40% long term corporate bonds; and 10% treasury bills, with expense loadings of 1.50% for stocks; 0.50% for bonds; and 0.30% for cash), Hebeler provides average returns for the portfolio, the accumulating investor, and the distributing investor, as well as the results of 80% percentile returns (reflecting desires for portfolio survivability for retirement distributions). One should also note that indexing the portfolios would add 0.70% to each portfolio's returns simply due to reduced costs.

Value averaging
Caveat: Value Averaging is an advanced investing topic. Investors may need to hold funds in reserve, such as a money market fund, in order to supply additional contributions needed during market declines. Management of this cash flow will add to the complexity of this technique. Please ask in the forum for assistance.

The technique of Value averaging was first promulgated by former Harvard professor, Michael E. Edelson, in his book, Value Averaging, published by Wiley in 1988. . Conceptually, value averaging can be thought of as combining the attributes of both dollar cost averaging and portfolio rebalancing. Value averaging is based on a formula (see quote box for details) which guides how much one invests into a given investment at a specific time. Value averaging seeks to increase the investment's value by this calculated amount on a periodic basis.

The following spreadsheet table compares Value averaging and Dollar cost averaging:

Here are some qualifying cautions to consider regarding value averaging :


 * Value averaging adds a growth factor (by formula, consisting of estimates of both the investment's return as well as growth in the contribution level) to the regular periodic investment of savings flows. If an investor's contribution amount is not expected to grow, this factor should be set at 0% so that investment growth is the sole growth variable.
 * Value averaging may require both purchases and sales of the underlying investment, based on the investment performance of the investment. The strategy requires a cash account for holding prospective purchases as well as any sales proceeds.
 * Value averaging sales can result in realizing taxable gains. Thus, one might restrict the strategy to tax advantaged accounts; or alternately, adopt a policy constraint forbidding or delaying sales in the taxable account.
 * You have to be careful in a declining market, as you will need to have additional funds available for investment. As time progresses and the account value grows, you may need even more funds to reach the amount required for the chosen period. If the market is volatile near the end of the investing time frame, you will need a lot of additional funds. This may catch investors unprepared for this additional savings requirement.
 * Value averaging most often provides a lower average cost per share than does DCA, and also provides for a higher internal rate of return (IRR). This does not, however, mean that value averaging will result in a higher net return.

Dollar cost averaging

 * Dollar cost averaging definition, investopedia
 * Dollar Cost Averaging, video Fama/French Forum
 * Does Dollar Cost Averaging Really Work, DCA calculator, moneychimp
 * Do Not Dollar-Cost-Average for More than Twelve Months Bill Jones, Efficient Frontier, October 1997
 * Dollar Cost Averaging, detailed examination by Sigma Investing

Value averaging

 * Choosing Between Dollar-Cost And Value Averaging, investopedia
 * Value Averaging, detailed examination by Sigma Investing
 * DCA vs. VA, gummy stuff
 * How Value Averaging adds Value, Bruce Ramsey (November 15, 2010)
 * Wiley: Value Averaging: The Safe and and Easy Strategy for Higher Investment Returns, links to value averaging spreadsheets