My wife has had ILR for almost 12 months now and we are considering applying for citizenship.

I would like some clarity on the residential qualifying period if possible.

Would the qualifying period have started when she was granted her 2yr spouse visa? so she can apply after having ILR for 12 months and therefore serving three years.

Or, does the qualifying period start from the date she was granted ILR?

http://www.ukba.homeoffice.gov.uk/britishcitizenship/eligibility/naturalisation/spouseorcivilpartnerofcitizen/

For most it starts when they first enter the UK with their spouse visa.

However, if legally in the UK prior to this, e.g. as a visitor, then it could start even earlier.

The requirement for the spouse or civil partner of a British citizen is that they were legally in the UK on the exact date three years prior to submitting their application, the type of visa held at that time doesn't matter, and during the past three years have spent a maximum of 270 days out of the UK with no more than 90 days in the final year.