Dividend investors rely on regular payments from the stocks that they own. Yet some stocks don't just give their shareholders money every few months, instead supplementing their payouts from time to time with additional special dividends.

Special dividends can be extremely lucrative, but they're not always predictable. With that in mind, below you'll learn more about what Costco Wholesale (NASDAQ:COST), PACCAR (NASDAQ:PCAR), and CME Group (NASDAQ:CME) have done for their shareholders lately in terms of paying special dividends -- and whether investors can expect a repeat performance in 2018.

Stock

Special Dividend Date and Amount

Regular Dividend (Annual)

Costco Wholesale

May 8, $7

$2

PACCAR

Dec. 13, $1.20

$1

CME Group

Dec. 27, $3.50

$2.64

Data source: Yahoo! Finance. Date reflects ex-dividend date. Amounts are per share.

Shopping for higher dividends

Costco announced in April that it would pay a special dividend of $7 per share to its investors. That amount represented about 4% of the stock's price when it was announced. Even though Costco raised its regular dividend at the same time, the $7 per share special payout provided a nice supplement to the $0.50 per share that it said it would pay out going forward, which worked out to a regular dividend yield of just over 1%.

CFO Richard Galanti referred to the move as "our latest step in returning capital to our shareholders," citing "our strong balance sheet and favorable access to the credit markets" in making the dividend possible. The special dividend wasn't Costco's first, having paid out dividends of $7 in late 2012 and $5 in mid-2015. By structuring the bulk of its payouts this way, Costco retains flexibility to deliver income back to shareholders without making implicit promises of sustaining regular payouts that a cyclical downturn could force it to break.

PACCAR drives forward with a special dividend

More recently, PACCAR joined the crowd with a special dividend of $1.20 per share. Shareholders in the truck manufacturer received their payment in early January, with the amount working out to about 1.5% of its share price. That more than doubled the effective dividend yield, given the $0.25 per share quarterly payout that PACCAR makes on a regular basis.

What makes PACCAR's special dividend a bit different is that the company quite reliably makes a special payment at the end of each year. Over the course of the past 20 years, the company paid 19 year-end special dividends, missing only 2009, before which it had cut its dividend in half in light of the aftermath of the financial crisis and 2008 recession. For PACCAR shareholders, the only question in their minds is how much the special dividend will be each year, and with a range of $0.60 to $1.40 per share since 2011, 2017's payout was at the upper end of the range, reflecting solid conditions for PACCAR's business.

Calculator, glasses, money, and a notebook with Dividends written in it, all on a desk surface.

Image source: Getty Images.

CME also gives dividend investors a double

CME Group shares a similar practice as PACCAR, and it goes a step further in recognizing that the move no longer comes as a surprise to shareholders, calling it an "annual variable dividend" instead of a special dividend. The 2017 installment came to $3.50 per share, which was more than 2% of the company's share price at the time of the announcement and more than doubles the annual payout from its regular $0.66-per-share quarterly dividends. Shareholders received their latest special dividend in mid-January.

CME started its practice of annual supplemental dividends back in early 2012, and the amounts have gone from the initial $0.60-per-share payment to the most recent amount of nearly six times that first annual special dividend. The exchange's intention is to base the dividend on the amount of excess cash available to the business each year, giving it the option to increase or decrease the amount based on capital needs and operating results. So far, that's worked out well for investors, and with many hoping for new growth for the exchange, further dividend increases could follow.

Be smart about special dividends

The nature of special dividends means that you can't count on them the same way that most dividend investors expect regular dividends to keep coming in quarter after quarter. Nevertheless, CME Group, PACCAR, and Costco Wholesale have all had a history of recurring special dividends. PACCAR and CME are likely to do additional year-end special dividends at the end of 2018, but for Costco, it would be unusual to do another special payout so soon after its most recent one.

Dan Caplinger has no position in any of the stocks mentioned. The Motley Fool owns shares of Paccar. The Motley Fool recommends CME Group and Costco Wholesale. The Motley Fool has a disclosure policy.