Chiming in with helpful rules of thumb I go by:
1. Never give an estimate in the same conversation in which it was requested, unless you're quite sure the answer is "less than an hour". Especially if they are going to turn around and quote your timeframe to a customer. The reason for this rule is:
2. The more you think about an estimate, the higher it will go. "Oh yeah and we'll also have to..." is 100x more common than "I found a shortcut that doesn't compromise on..."
3. Even if they know it's an estimate and not a deadline, they might not know the difference between "40 hours of dedicated effort" and "One week's worth of business hours". Making that distinction is just as important as the estimate/deadline distinction.
I'm lucky to work where we don't spend much effort on estimates and time tracking, both of which just make things take longer and cause productivity-reducing stress.
The distinction between labor time and calendar time is an important one! 40 hours of dedicated effort is great, but most people parse that as "1 week" when in reality the available people may only be able to get 10 or 20 hours in a week due to other demands, or it's 38 hours of dedicated time that gets done in 1 week but the 2 hours of security and legal reviews take a month of waiting to finally get completed.
I call it lead time and labor time.
1FTE labor will be x hours but lead time can be couple weeks depending on where are we in development cycle.
When I switched from engineering to management, I spent a long time thinking about software estimates, read about many different approaches, and argued with many other managers (I’ll try to write up my own blog post for the next time the topic comes up on here).
The framing in this blog post is better than some (it at least discusses uncertainty) but I believe it’s still basically the wrong framework.
People (managers) like to assume that estimates are a random variable, and software projects are samples from project space. Estimates can be produced for a project by analogizing it to similar projects. This is not true at all. You cannot reason about software projects by analogy.
Some assertions (that I will explore in said promised blog post):
- Software development is chaotic: arbitrarily small changes in the input (project requirements, who’s implementing it, stakeholders, team, etc) may lead to arbitrarily large changes in time-to-completion (including “this project is now impossible”). In short, any project may explode at any moment prior to completion.
- The risk of a project is particularly sensitive to the engineer implementing it, and depends on that person’s specific knowledge. Have they used these APIs or this database before? Any part of a project that the engineer hasn’t used before represents potentially unbounded technical risk.
- the way to manage this risk is to include buffer in the project timeline, and, critically, to use that buffer not for development tasks that were harder than expected, but for re-planning and re-negotiating the deliverables with stakeholders, to un-explode the project. Agile builds this re-evaluation into the project lifecycle, which is the main (maybe only?) thing is does really right.
I agree that the points you raise are important to realise and affect delivery duration significantly.
I, however, disagree with that approach to managing delivery: if you tie in expected value with deliverables, you empower and enable engineering teams to smartly cut scope and deliver in shorter amount of time the biggest chunk of the value.
It's usually only described as "cutting scope", but it requires real creativity and smarts on the engineering team (they can best tell what's feasible in remaining time, when they have tackled all the unknown unknowns you bring up) to do that in a way that still brings the most of the original value. If you move this to your "renegotiation" step, it becomes too slow and hurts delivery as well.
I basically agree (I think) in that I don’t think there needs to be a separate “cutting scope” phase—one should it as soon as they realize they need to. And I certainly agree that it’s incumbent on engineering to invent alternatives and propose them when we realize that we need to cut scope (for the reasons you mentioned).
FWIW, though, engineers shouldn’t decide what to cut (i.e. choose alternatives) in a vacuum, in my experience. I’ve been in plenty of meetings with product/sales/support where they say “it’s better for the whole project to slip than to release it without this one detail” or “we would give up what seems like basic usability to get one particular piece of polish”
Yes, totally agreed that engineers should not "decide" in a vacuum.
But if they understand what value was supposed to be brought, have a decent product/customer focus, and are creative enough, they can propose good alternatives and not stall the delivery.
I've also experienced things you mention, but it was always in orgs where everything, including any small feature, was treated as a "big bet": unsupported by metrics (no matter how imperfect), but instead wishful thinking that it will bring meaningful improvement. As such, you can't come up with anything that's an equally good improvement with less effort because there is no baseline to compare against.
I find your framing interesting. But most importantly, even if nothing changes in the requirements or the team, the mere new information that is learned while implementing the project is often enough to change the estimate considerably.
Yes! In my last role, I aggressively pushed the concept of “technical risk” to try and get people used to this idea.
Sometimes the computers don’t work the way you thought they did at the beginning. This is a normal and ubiquitous form of risk that just needs to be managed like any other type of risk, with prototypes, multiple revisions of the implementation (each introducing additional risk), occasionally re-scoping, etc.
People outside engineering sometimes don’t like it because the risk is human in origin—it comes from engineers not knowing things, and our job is to know things—but until there’s an omniscient engineer, this risk will continue to exist.
Yes, this fits my experience as well.
Oftentimes I've heard people who are not and have never been software engineers ask "When we want to built a bridge, engineers can tell how long it will take and how expensive it will be, how come with software engineers it's never the case?" (often implied: you software engineers have it easy, slackers! -- I believe we put this blame on ourselves with our immature culture, but that's another discussion)
What I usually answer to that is that, to begin with, that if they had actually dealed with big construction projects like bridges then they would not idealize those so much. And secondly, that this is not the right analogy. Bridge construction is a much stabler science, it had no "complexity explosion". A better analogy would be geophysical prospection : the theory it's based on is sound and mature but the unknowns dominate everything in predicting the outcome.
- the way to manage this risk is to include buffer in the project timeline, and, critically, to use that buffer not for development tasks that were harder than expected, but for re-planning and re-negotiating the deliverables with stakeholders, to un-explode the project. Agile builds this re-evaluation into the project lifecycle, which is the main (maybe only?) thing is does really right.
This is the only right answer. Unfortunately, engineering leadership is too detached from understanding how software works. They think of projects like contractor painting jobs. So easy to estimate - sq. ft * number of people * number of hours.
But software is not like that. Software is constantly changing every hour, every day. As a result, any estimation is changing every hour every day.
The best thing is for leadership to start acknowledging the realm they are dealing with. If they can't they should step down.
But realistically, engineers should always give 400% padding with estimates. The root cause of this estimation is poor leadership. It is not engineering team's problem that detached management doesn't understand software.
That's too much of a carrot IMHO: I would have appreciated it more if you dove deeper into one of those points instead of promising a blog post on a dozen.
Edit: thanks for editing the comment to make it clearer what are your points. This makes my comment somewhat useless :)
> When you're communicating an estimate the most likely mistake is that the other party considers it to be a commitment.
The root cause is typically that you're communicating it to someone who doesn't want an estimate. In that case, communicating the estimate with the commitment is often a mistake unless you're willing to negotiate the commitment, because that's effectively what it invites.
The best estimates I’ve found are “This will take: days, weeks, months, years”. No numeric values allowed. Yes, you can’t do (inherently faulty) math on these estimates to arrive at aggregate metrics: this is a feature. However, it still allows you to meaningfully schedule work.
If pushed, I get my developers to give estimates in jumps of ~5x.
Their options are
2 days
2 weeks
2 months
10 months
Then I triple the estimates before sharing with the business.
We don't estimate individual tickets/bugs at all, just overarching projects.
I also ask the business to estimate the commercial/user impact of the projects too, and we track and report the reality against their estimate, to hold a bit of a mirror up to them and as a way of pushing back on doing pointless work. Those estimates we use similar orders of magnitude for - £1k, £10k, £100k, £1m, £10m.
Fermi estimations like these really help avoid protracted negotiations and the lack of precision is a feature that makes clear they are estimated.
What is an estimate for? It is really an estimate of cost where big-O is mostly developer cost and that gives a handle on the next part priority.
Both of these then add up to an illusion of control.
Software is quickly becoming the largest moving part of many many organisations - and trying to control it is likely the wrong approach
Software is a form of capital just like a robot on the Tesla assembly line. That robot and the software being estimated in the article are to do a specific job in a specific environment- an investment that will enable more production than without.
But all capital rots - or rather depreciates. Taking a nice view you can have 10% on maintenance and repairs (but realistically more than that).
Don’t try to estimate these - don’t ask your handyman for a Gantt chart for a hundred tiny fixes - just get them done.
Generally good advice, however I think the actual example phrases could still be clarified, e.g. bg explaining why clear estimates in software engineering are not as common as in other fields — note the person you are talking to might have a completely different experience in their field of work. And then you give your buest guess and a clear explaination of your level of confidence, which factors could lead to shorter or longer project durations.
A more interesting question is how you follow up on your estimates? How can you improve if you don't track and reflect on the actual result on what was estimated?
Combining Software time/cost estimates with value estimates make it even more fun, because most software is low value (with some chance of being extremely valuable). Combining these into an ROI probability space makes everybody sad, but the expected value is still positive even if the most likely outcome is software that wasn't really worth paying for!
An estimate is really a probability distribution, that often resembles a Gaussian distribution and thus can be captured with two numbers: the average and the variance. Combining multiple estimates together would involve some math around these two numbers. But the surprising thing is that managers in the software industry don't really understand probabilities, and to make it understandable those managers want to reduce the model to just one number, and when this model fails to capture the probabilistic nature of the underlying process, they attempt to overrule the math with authority.
>they attempt to overrule the math with authority
It’s entirely possible to turn that to your advantage, but takes some luck/skill, not dissimilar to profiting off of stock market crashes.
The asymmetry between mathematics and authority tends to favour the math.
Having run a software team with good estimates, I’m disappointed in some of the commentary of, “just make up a long or obscure estimate.” I don’t expect a considerable amount of unknowns to come up in a project unless you have changing requirements or bad planning.
You can’t do anything about changing requirements so that can be forgiven. Poor planning cannot though.
Unreasonable stakeholders will absolutely hold you accountable to not meeting a schedule even when they're constantly changing requirements. And they can and will throw you under the bus for it.
You are right though, that a decent team that does decent planning should be fairly accurate much of the time. And there are project management techniques to handle the remaining uncertainty.
If requirements change estimates change as well.
In theory, yes.
In practice, if you try to change the estimate, you'll be shot down and asked to work harder. The people changing the requirements assume that software is infinitely malleable and any change is doable with a small amount of effort. After all the devs are smart so they'll figure it out, like they always do. To these people, asking for a change in estimate is indistinguishable from complaining or being lazy.
Yes, but stakeholders may not accept them... which is their problem, but they can make it your problem.
It usually centers on whether changing requirements are due to poor planning or not?
I don't necessarily think it is, and I believe it's easily fixed by keeping the reason (expected value) for anything close to any requirements being passed down to engineering teams.
Bad companies demand estimates.
Good companies just live by a Steam clock.
The best way to estimate:
"Wild guess - X weeks but could be X+Y weeks for unknown unknowns" (where X is 200% estimate in your mind and Y is 700% of estimate in your mind)