I'm pitching a new Asp.Net WebForms app to a client. Is it a fair statement to tell him it will easily have a 5-7 year life span? Meaning that I (or some other dev) could continue to enhance it for their business (as we know it today), and that he will be able to get Asp.Net web hosting accounts for it (or at least IT folks who still know how to do it in house), and a user experience that will be acceptable along the way before it seems too aged near the end of that 5th, 6th, or 7th year.

This is a rather plain LOB businesss app, not some super-duper Web 2.0 Ajax powered super crazy UI. Basic CRUD stuff in WebForms and some simple CSS. It's a functional thing, not a fancy thing.

I don't want to misslead him about the life of it, but I don't want to sell it short either like 3-5 years.


Surely a Webforms app built on .Net 3.5 (or 4.0 by the time this is deployed) can be expected to run in an acceptable fashion for 7 years from today.

Do I dare stretch it to "7-10 years"?