Contractors working with the government often have to estimate the amount of work to be performed in “person-years.” Person-years are used as a measure of how many hours a company is expected to contribute every year, yet it turns out that a single person-years is really difficult to define because there are so many variables.
Calculations of a person-year are complicated by vacation time, sick leaves, re-training periods, short term disabilities, pregnancies, or even military reserve duty.
Here is an excerpt from a report published in Public Spend Forum:
Let’s start with the basics — 2080 hours in a person year is equivalent to one person, working 40 hours a week for 52 weeks in a year. To be even more accurate, perhaps even to an annoying degree, 2087 hours would take into account leap years. While ideal, this is, of course, unrealistic because it doesn’t take into account any of the time off that employees will expect to receive throughout the year. 2000 is a bit more reasonable, taking into account the 10 national holidays, but it still leaves no room for vacations, or sick, emergency, and pregnancy leave. 1920 would be even better, as it leaves room for not only two weeks leave for holidays, but also 2 weeks to fulfill any other needs for time off. Something even lower, like 1860, could also be used to take into account more of the variables listed above. One survey suggested that most service industries, even outside of government contract work, required employees to bill at least 31 hours per week, which would whittle the figure of person hours per year down to 1612 — which does not include holidays or vacations. With holidays and vacations included, this figure would become 1519.
How many hours should be in a person year? You now have some options listed above, but which is the right one? To make a long story short, there is no single correct answer. The last couple options seem like they can be ruled out right away as entirely too low, and the first couple seems entirely too high — and that instinct may not be wrong, but ultimately, the decision depends on the specific contract and specific employer.
In an ideal world, there would be a perfect, beautiful number that could equate to a person year for contracting service companies. Unfortunately, though, the world we inhabit is far from ideal, and so we must deal with the tangled complexities of the process of human living. There is no correct number for person year — the best you can do is keep your channel of communication open with the company, consider all possible factors, and combine all your knowledge and expertise of workplaces to come up with an estimate that might — just might — work for the contract. For a problem with such high stakes, it is not a very satisfying answer, but it ultimately reflects the real world.