While underpromising and overdelivering might seem like a good tactic to delight your customers because you want to have some buffer, don’t. There’s another way.
You can be open and honest —that’s the core of business, right? Being honest with your customers— and say you don’t know exactly how long or how much exactly it’ll take.
That you’ll put in some buffer, just in case.
Sure, you can give an estimate of the time, or even a timeline. Just please don’t lie.
Friend-of-the-list Jonathan Stark wrote this, if you need some help with how to say it (bold mine):
““There are many unknowns at this stage, but I’d be happy to draft a timeline with the known dependencies. This will be a living document that we can review and update on our weekly calls. The timeline will give you visibility into, and some control over the process. It will likely expand quickly in the early stages but over time the velocity of change will decrease and a reasonable delivery date will start to come into focus.”
While you’re at it, you could consider mentioning that anyone who promises to meet their arbitrary deadline is probably doing so out of inexperience or opportunism.”
You can always delight just by keeping to your word.
Unless you’re charging by the hour… then that is another story.