Estimating Ongoing Application Support

A great deal would depend on a number of factors.

1) how mature is the product. A new version of an existing product is much cheaper to support than a brand new product.

2) Background technology. If the product is based on a well know toolset -i.e SAP or Oracle, then there may already be a fair amount of info available as support collateral.

3) Level of documentation. The more care and effort put into good user docs and training material, the few call, less support.

4)Maturity and Breadth of support. A good support team will always be striving to reduce the number of calls, often by diverting people to other sources like websites, tutorials etc. New Products may or may not have all this collateral. Also the tenure of the team has a huge impact. Experienced support team members are usually more productive.

James

After all if you can't make gnerate revenus supporting it, it probably wasn't worth writing in the first place.
Seriously software providers in general plan on making more money from the support / upgrade stream than they do on the initial investment.

Presumably you are talkng about a purchase, if so there are a lot of factors.
How close a fit was it.
How stable(fixed) is the solution
Documentation levels
Technical support costs (Hardware, administration etc.
Training requirements
Platform longevity.
Inter-operability/compliance requirements

If you have outstanding quality control, extensive pre-release usability testing, and rigorous end-user training, then support costs will be minimal. This is how I develop software, and my phone almost never rings with a support call. The problem with this approach is that you can't measure and report the support costs you avoided because the software isn't crashing regularly.

On the other hand, if managment opted to underfund the development cycle, then going forward they can probably expect to spend a substantial portion of the full development budget again each year in support costs -- 50% or more. In this scenario I wouldn't even refer to this as "Support". It needs to be presented to management as "Deferred Development Cost" since you're having the end-users debug the product and find the design and coding errors.