estimation – Jim Grey

By Jim Grey (about)

Maybe you’re one of the lucky ones.

Maybe you work in a shop that executes scrum well. Your team keeps the backlog well groomed, understands its velocity, and delivers working software sprint after sprint. Or maybe you work in an open research-and-development shop where the journey is as important as the result, and projects are always open-ended.

If, like me, you have to deliver software on deadline using a less-than-perfectly executed methodology, this post is for you. It’s going to give you a technique for knowing where you stand against your deadlines – a very useful skill that will reduce the chaos you experience and help your boss steer projects more successfully, both of which are good for you.

It is a method for implementing continuous reestimation, which I wrote about in this post. Read it to know why this will make you and your boss more effective.

Teams that have worked for me and have estimated using this technique have seen their projects come in within estimate about 80% of the time. The other 20% of the time, they learned important things about their work that let them estimate more accurately the next time.

Here’s the technique:

Break down your work into tasks.
Estimate the tasks using a three-point formula.
As you work, reestimate every day.

Break down your work into tasks

You might resist this step because in your core you know you will miss some tasks. It’s okay. This process honors that you don’t know what you don’t know. Just outline the tasks as best you can.

But think small, because you’ll be more accurate when you estimate more small things than fewer big things. Break things down as small as you reasonably can.

Estimate the tasks using a three-point formula

For each task, then, think of the following:

If everything goes right on that task, how long will it take? This is the best case, B.
If everything goes wrong on that task, how long will it take? This is the worst case, W.
If a reasonable amount of things go wrong on that task, how long will it take? This is the likely case, L.

Think for a minute or two about each task, but any more than that is probably overthinking it.

Important: Calculate your estimates in hours. Not days, not weeks, hours. There’s too much slush in days and weeks. Besides, in an 8-hour day you probably work just 6 hours on project tasks. You spend the other two hours in meetings, having hallway conversations, using the restroom, and being interrupted.

Here is where some magic comes in. Just go with me on this. For each task, drop B, W, and L into this formula and calculate the answer.

$\displaystyle Estimate=\frac{B+4L+W}{6}$

You’re weighting the likely case, but honoring the best and worst cases – and in one deft motion you take fear out of your estimates. What makes estimates bad is either unexpected things happening or overpadding for unexpected things happening. Thinking best/likely/worst helps you be more objective. And when you add up these three-point estimates for all your tasks, you get a reasonable cushion for the things that could go wrong.

Divide the number of hours by the number of hours per day or week you will work on the project. Lay that number of days out on a calendar; tell your boss that’s when you’ll be done.

As you work, reestimate every day

You are going to discover tasks you didn’t think of at first. And some tasks are going to take longer than you originally thought. When this happens, estimate the new tasks and/or reestimate the task that’s taking longer. Recalculate your end date and break the news to your boss.

Your boss ought to kiss you right then and there, by the way, because you gave him or her information early enough to do something about it – adjust scope, add resources, move the date, or tell you that unfortunately you are looking at some late nights. Hopefully the answer will be a, b, or c more often than d.

And every time you have to reestimate, you’ve learned something about your work that helps you estimate more accurately in the future.

By Jim Grey (about)

Not long ago a software developer I work with suggested that building software could not, and so should not, be managed to a delivery date. “You can’t know everything you’re going to encounter while you build it,” he said, “and so it just takes the time it takes to get it done.”

I said that I agreed: you don’t know what you don’t know, and the work takes the time it takes. But I couldn’t agree that projects should be open-ended, finishing when they finish.

Capitalism interferes. Pesky, pesky capitalism.

Most of us make software that achieves some corporate goal about making piles of money. Because the company has plans for that money, it needs to know when it will start rolling in. The money can’t start rolling in until you ship.

Or maybe you’re making a prototype that will be demoed at a trade show in hopes of attracting investors, or you’re fixing a batch of bugs that have angered a key customer who is threatening to walk, or you have to deliver some fixes to comply with some new regulation that’s about to go into effect. Point is, your company has good reasons to ask when you’ll ship.

So you need to set expectations about the size and duration of your work. But fortunately, these guesses don’t have to lock you in and enslave you to your keyboard. That’s because every day you can check your progress, adjust for the things you’ve learned, and see if you need to set new expectations.

You’re driving to a destination

Getting your work done is a lot like taking a road trip. I love road trips! You never know what you’re going to encounter. Road construction, bad weather, mechanical failure, and even fun roadside attractions can all slow you down. You have to steer your way through all of these things.

When you’re on the road, it’s pretty easy to know at any time about when you’ll get where you’re going. It involves answering these three questions:

How will you know when you get where you’re going? On the road, you just recognize your destination. But I’m going to fit this metaphor to your work, where it isn’t always as clear what it means to arrive.
How far do you have left to go? Watch the signs; they’ll tell you.
How fast are you going? Just check your speedometer.

Every time you see a sign, divide the number of miles to go by your average speed, and you have the best case for how long it will take to arrive. You can’t control what might go wrong on the road ahead, of course. But after something on the road does slow you down, you can just recalculate and get a new arrival time.

You can manage your own work in much the same way. But it means you have to build some skill at estimating.

“Uh, two weeks”

Here’s how not to estimate. My first post-college job was as a technical writer in a software company. My first assignment was to convert a thick product manual from an old publishing platform to a new one. It was hardly a mission-critical project, but I was green.

When the boss asked when I’d be done, I had no idea, so I shrugged and said, “Uh, two weeks.” Then the task turned out to be enormous and tedious. I had to put in a ton of extra time to finish in two weeks.

When my boss asked “how long” on my next assignment, I guessed a number – and then doubled it to account for the unknown. Success! I worked no extra time and finished my project before the deadline.

Except that I hadn’t learned anything of value. My “guess” estimating technique became “guess and pad like crazy.” And I still had the problem that if I didn’t pad enough, my only recourse was to work tons of extra hours. I had no way of knowing on any given day whether I was on track to finish when I said I would. I just had to work hard and hope.

It’s okay that you don’t know what you don’t know

If I could tell my 21-year-old self something, it would be this: Ask the boss if you can get back to him in two days. Then use your two days to do this:

Think about what done looks like. What must you do to finish the work? How will you know when you’ve gotten through it all? In this case, I had about the easiest possible situation: “Done” meant running out of pages to convert. You may have a number of requirements to code, or a batch of test charters to execute, or a set of stories to complete – there are any number of ways to chunk the work.
Do some of the work. Pay attention to how many chunks you complete in your two days. Then note how many chunks you have left. There’s your speedometer and your miles-to-go sign. Divide to get your rate: chunks per hour or chunks per day.
Calculate how long the rest of the work will take. Divide your rate into the number of remaining chunks. Lay that number out on a calendar to find your finish date. Tell that to the boss.

And then as you work, recalculate every day based on how much you got done that day. If you need to put in a few extra hours to stay on track, just do it. But when the amount of extra effort needed to stay on track starts to edge toward heroic, it’s time to negotiate.

That’s right, negotiate. You are the master of your own work, after all; nobody knows the reality of it better than you. Your estimate is what you believe it takes to reach Done, and you need to stand up for it. This is true, by the way, even when your boss has given you a due date.

So go to the boss and ask which is more important: the due date or this body of work? In other words, can you change what it means to be done, removing enough work to hit the date? Or can you move the date out to get all the work done? Or can you do a little of both?

Sometimes the answer to this question doesn’t go far enough to make the remaining work match the due date. So ask yourself if you can give some of the work to someone else, enough to hit the due date. If so, ask for people to help you.

What you’re doing is giving the boss and all of your project’s stakeholders as much runway as possible to understand the probability that you’ll deliver the originally defined Done on time. Should that probability drop, your negotiations give them the opportunity to change course, change expectations, or both.

Sometimes, you’ll get no answers to all of these questions. Sometimes, you’ll get yes answers to some or all of them and it still won’t be enough. But asking these questions is your best chance of avoiding working heroic hours.

An estimate should not be a commitment

If no is always the answer, or your bosses just expect you to rise heroically to every occasion, or your initial estimate is interpreted as a contract or an iron-clad promise, you just might be an in environment with dysfunctional beliefs about accountability. Consider finding another place to work.

Your estimate is only your best (and, hopefully, educated) view into when you will finish. It assumes that you don’t know what you don’t know. When you learn more, your estimate is obviously going to change. You’re better off working someplace that has at least an elementary understanding of this.

And now you understand it. Estimate based on what you do know. Go ahead and pad a little (a little!) for the unknown.

But then steer your work to successful completion.

I thank my brother, Rick Grey, who tests software for his supper, for contributing several key concepts to this post.