The original poster asked the following:
Should Agile Projects cost more/less than waterfall projects?and the answers varied greatly!
The following focused on whether this was a valid question:
Proving an Agile project is less costly is not easy because your attempting to compare an alternative history -- Clay Nelson
...if we ever start to sell Agile as a way to lower costs then we just invite a a backlash against Agile -- David NesslAnd others attempted to answer it:
Agile does not aim to be a low-cost alternative. Some seem to believe so, but the aim is agility: Speed and flexibility. We become agile to shorten time to market, to increase adaptability and reap greater ROI over the lifetime of a product, to name a few reasons. -- Marcus Widerberg
Agile should cost less for several reasons, among which are: Your mistakes cost less... Earlier opportunities to start getting ROI... Failing early vs Failing late... -- Chuck van der LindenAnd of course... my answer:
Most companies do a horrible job of measuring the quality and defect costs that start during the integration/testing/stabilization phases running all the way through support. All companies do a horrible job of measuring technical debt.
If agile reduces these up front, then overall Agile is cheaper from an end-to-end perspective.
But since nobody knows or tracks the cost of these things, Agile (which takes more effort/work to be successful at) will look more expensive on paper.
Tech Example: I can write code without automated tests in half the time, but what will it cost later?
Business Example: I can plan and design everything now, but what will be the cost of unknowns and market changes later when I can't handle it?
Oh, by the way, Forrester Research did a partner study with Thoughtworks... "Forrester TEI concluded our Agile delivery is 40% less expensive overall". - from a Ross Pettit presentation @ Agile East 2009