Does the ‘man month’ metric still work in today’s world?

Early on in my project management life I read a book that described what a ‘man-month’ or ‘man-day’ is, which is paraphrased as the amount of productive time you can expect from an employee given a defined period.  Six hours of an eight hour day is the general rule of thumb.  This gives you about 120 hours each month of productive work.  Believe it or not, this metric is still a pretty decent way to estimate expected billable hours in a year per consultant – 1440 hours.  It is very basic but effective to conservatively estimate your capacity.

What about using a more complex and scientific metrics approach to define productivity?  Let’s say your organization is tracking administration time, vacation time, holidays, and travel time as overhead for adjusting productivity and expected billable contribution.  As an experiment, I decided to use data from my own organization and here’s what I came up with:

• Average monthly Administration time which includes company meetings, non-billable client work, research, timesheets/expenses, etc. is about 21 hours.   I removed bench time since this doesn’t represent any working time.
• Average travel time each month is about 17 hours
• Vacation time allotment each year is 120 hours total
• Holidays observed by the company each year is 8 which equates to 64 hours total

My company observes a 40 hour work week which equates to 2080 hours in a year.  Now let’s apply the metrics above and see what the final adjustment for productivity would be:

• 2080 hrs
• – 252 hours Admin
• – 204 hours travel time
• – 120 vacation hours
• – 64 holiday hours

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1440 hours productive in a year

OK, that is amazing!  I’m sure if you looked closer at my timesheets you may have a few hours either way that should be included or excluded.  It’s all how you define and capture metrics (aren’t numbers wonderful?).   You may have noticed I didn’t include sales time.  I consider sales consider productive time simply because it is a means to an end to close new business.  Investment in sales is a necessity.

What I should point out is that these productive numbers are still based on an expected work week definition – 40 hours in this example.  In the world of ‘salaried employees’ a 40 hour work week almost seems unheard of, unless it’s the week you take off for vacation.   Typically a 45 to 50 hour work week is pretty common, and even more depending on your industry.  So why not just make the work week definition higher?  9 hours per day?  10 hours per day?   My theory is that increasing the hours in a day will not actually increase your productivity in a day.  It just makes for a longer day with more breaks to avoid burning out your team.  When deadlines loom large, your team most likely steps up to the plate, works long hours and weekends, and earns a sense of pride when the deadline is accomplished.  Sustaining this type of work schedule is difficult and hard on employees – definitely don’t make a capacity plan around this level of effort.

So sometimes the simple method is actually a decent method to follow – such as the ‘man month’ metric (ok, person-month if you want to be more P.C.).  Capture your own set of metrics to confirm or perhaps your metrics will guide you into something even more conservative for consideration.  For companies with trending data, this exercise is well worth it to understand and predict behavior in a billable environment.  Try it out and see for yourself – I’m just sayin’.