Iterative vs Incremental Flashcard

Sometimes, the difference between incremental and iterative (software) product development is subtle. Often it is crucial to unlocking early value or quickly eliminating risk – an iterative approach will do this for you, while incremental will not.

Incremental vs Iterative
Incremental vs Iterative

Let’s review the distinction. Incremental means building something piece by piece, like creating a picture by finishing a jigsaw puzzle. This is great for visibility of progress, especially if you make the pieces very small. However, the inherent risk is that an incremental build is not done until the last piece is in place. Splitting something into incremental pieces implies the finished whole is understood (by the jigsaw designer, at least). If something changes during the build, like a bump to the table,  all of your work to date is at risk. Future work – to finish the whole – is also at risk of delivering less than optimal value, if our understanding of value changes during an incremental build. Much development work done under an agile banner is in fact incremental, and therefore more like a mini-waterfall approach than an essentially agile approach.

Iterative, on the other hand, means building something through successive refinements, starting from the crudest implementation that will do the job, and at each stage refining in such a way that you maintain a coherent whole. You might think of this like playing Pictionary. When you are asked to draw the Mona Lisa, you start with (perhaps) a rectangle with a circle inside. If your partner guesses at this point, great! If not, you might add the smile, the hair, the eyes. Hopefully, your partner has guessed by now.  If not, embellish the frame, add the landscape, draw da Vinci painting it, show it hanging in the Louvre, etc. Your risk exposure (that time will expire before your partner guesses) is far lower with an iterative approach. With each iteration, you have captured some value. If your understanding of value changes (eg, your partner shouts something unhelpful like “stockade”), you still retain your captured value, and you can also adjust your future activities to accommodate your new understanding.

I think I capture all of this in the diagram above. If you’re having trouble articulating the difference between incremental and iterative (because both show similar signs of progress at times), or you’re concerned about the risk profile of your delivery, refer to this handy pocket guide.

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