Though we all have a gut-sense that working too many hours is counterproductive, a very short paper by John Nevison called "Overtime Hours: The Rule of Fifty" at Project Solutions (where you need to register) cites data from four studies conducted over a half century to show how productivity either drops, or at best maxes out, as overtime increases.

The studies' results vary quite a bit. One shows that at 50 hours/week workers do about 37 hours work, dropping to just over 30 once the workweek increases to 55. The "best," if you can call it that, results were from a 1997 survey showed wielding the whip can have ever-increasing productive rewards, edging up to about 52 productive hours for a 70 hour week. But they all show a nearly-impenetrable barrier of around 50 useful hours or less, regardless of overtime.

Unsurprisingly the data shows a sharp drop in results for those working excessive OT for weeks on end, averaging around a 20% drop after 12 weeks of servitude. That means, as the author concludes, the Rule of Fifty is a best case estimate.

The 2005 Circadian Technologies Shiftware Practices survey showed that productivity can decrease by as much as 25% for a 60 hour workweek, which jibes pretty well with Nevison's data. Circadian's results also demonstrate that turnover is nearly three times higher among workers putting in a lot of OT, and absenteeism is twice the national average. I'm not sure what that result means, since it's awfully hard for an absent worker to be putting in overtime.

Fred Brooks claims that the average software engineer devotes about 55% of his week to project work. The rest goes to overhead activities, responding to HR, meetings about the health insurance plan, and supporting other activities.

The German Embassy's Washington  web site claims on its web  site that the nominal workweek in Germany is 37.5 hours because "The original reason for introducing this system was to combat rush-hour traffic congestion, but among the more direct gains are an improvement in employee morale, greater productivity, significant decreases in absenteeism, greater flexibility for women who juggle the demands of work, home and children, and the increased sense of individual dignity that the employees get from having a greater say in organizing their own time."

The last phrase may be true but seems awfully hard to measure. However, their conclusions about morale, absenteeism and productivity seem parallel the survey results quoted above.

What's your take? When does overtime become counterproductive?

Jack G. Ganssle is a lecturer and consultant on embedded development issues. He conducts seminars on embedded systems and helps companies with their embedded challenges. Contact him at jack@ganssle.com. His website is www.ganssle.com.