The company wants us to report the duration of the project in months. Based on how you calculate it, the duration can differ drastically.

Take a simple example in which the project starts on 1/1/2017 and ends on 1/1/2021.

It is easy to see how the duration is 4 years = 48 months.

However, there are 1461 days in this period which is 48.7 months!

Is there an accepted best practice on which value to report?


Ask, then document.

If 'the company' wants it reported in months, then ask 'the company' what that means.

And then document it as a standard. This is done both so you don't have to keep asking, and so that if 'the company' later complains, you can point to the documentation (which contains both the date and the name of who made the decision).


It seems you have answered your own question. If the start and end dates of a project are pre-determined, then you have your answer.

Consider helping your organization by determining the end result of the effort and help them track progress towards that end result. What is the point of this project? Breakdown the steps towards that end goal and show incremental progress toward it.

If your product has shifting requirements and/or shifting technology concerns then please consider an incremental approach. Instead of predicting an end result and a project deadline, consider that shifting concerns will invalidate any long-term prediction fairly quickly.

Instead, do the work of defining small bits of valuable delivery that you can make to the client. Added together, all these pieces would accomplish the overall goal of the project. Use frequent inspections of progress to adapt your approach to accomplishing each additional increment.


Your calculation assumes that all months average exactly 30 days in length. This is not the case!

In the example given, this issue is probably not that the calculation throws up a discrepancy of about 1.6% between two different ways of calculating the difference between dates: my concern is that you seem to be saying that there is a hard stop to the project in 4 years time. How have you reached that conclusion? It sounds too like you have based this on an assumption rather than knowing what the deliverables are and how they all fit together into a planned set of activities and actions - unless the project is something to do with something that is happening on that specific date. In which case, the issue is not the number of months, but rather how many resources you may need to deploy (and hence the costs you need to incur) to deliver on that date.

If, however, the discussion is about payment for the work, then it is down to clarification of the commercial arrangements. If you are paid by the month, regardless of length, then February (28 days) is a good month, and March is less good (31 days). If you are paid by the day, then the number of months doesn't matter. Either way, get it agreed and documented, and move on.

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