[xn]

Is it going to take more than two hours?

Is it going to take more than two days?

Is it going to take more than two weeks?

Is it going to take more than two months?

Is it going to take more than two years?

If you can answer these questions, you can estimate using a confidence interval.

If the estimate is too wide, break it down into smaller chunks, and re-estimate.

If you can't break it down further, decide whether it's worth spending time to gather information needed to narrow the estimate or break it down. If not, scrap the project.

[dchuk]

I prefer 1 hour/1 day/etc but yes, this is the only method that I’ve found to work. Be very clear what result you’re trying to produce, spec out the idea in detail, break down the spec into logical steps, use orders of magnitude to break down each step. There’s your estimate. If you can’t break it down enough to get into the 1 day/1 week range per step, you don’t actually have a plan and can’t produce a realistic estimate

[n4r9]

What if the project involves trying one approach for a week, then assessing whether that approach still looks viable vs moving onto a different approach? This happens a lot with challenging projects, you basically just keep trying different things until one works.

[xn]

Then you know that it's going to take at least, say two weeks, one week for the first implementation and a week to finish it if it works.

On the high end, could it take more than 2 years? 1 year? 6 months? Stop when you are 80% confident that it won't take longer than some period.

So your estimate might be between two weeks and six months. Is that an acceptable estimate for the "buyer"? If not, is it worth expending effort to narrow the estimate?

[scott_w]

There’s also something more concrete about asking “Can you get it done by end of tomorrow? What does that require?”

I prefer it over estimating which feels more like asking the length of a piece of string.

[alfiedotwtf]

The problem I have is, conceptually a task always looks easy, but then as your coding, you hit several problems that are not simple to overcome - in fact, lot of times these issues turn into almost insolvable problems that blow out any time estimates ;(

[swat535]

I like this approach, it's more accurate than T-shirt sizing.