Ideal time in Agile estimation

In an earlier post we looked at agile estimation using story points. Let us now look at another unit used in agile estimation, the ideal time.

What does ideal time mean and how is it different from the standard calendar time used to come up with schedules and determine project completion?

The standard calendar time is also referred to as elapsed time. In this post, let us refer to this as calendar time since that is a term that is more widely used. Ideal time is what the term implies - the ideal time it would take to complete an activity if there were no overheads. To further clarify, overheads refer to the time spent on unplanned activities such as checking emails, phone calls, attending meetings, switching between tasks, interruptions of any kind, etc. which are very much existent in any team member's day. For example, in an eight hour working day, the ideal time available to work on a planned task may actually be between four to five hours after accounting for overheads.

When seeking time based estimates from team members it is important to be clear on the unit used. Are your team members estimating in ideal time or calendar time. When a team member says it will take X days to complete an activity or story, does it mean X days exclusively working on nothing but this particular activity? Managers who mistakenly think that any time based estimates refer to calendar days may map the estimate to a calendar and have the wrong expectation.

When estimating in ideal time the assumption is you will solely and fully work on the particular task for the estimated duration without any interruption plus everything you need (such as tools, people, dependencies, etc.) are readily available for your use when you need it. Ideal time estimates are agnostic to the level of overheads in a particular environment and may be used to derive duration similar to how Story points are used.