Claiming the year you arrive in Ireland as part of the 5 years for naturalisation

I will be moving to Ireland later this year, and plan on staying. I'm a Brit but quite keen on getting naturalised. I have no Irish ancestors so this would be based on 5 years residence.

The document rules say you need 3 proofs of residence per year, and it shouldn't be too hard to collect those for 2019, but then when would my 5 year qualifying period end? Surely I can't claim for all of 2019 when I wasn't in Ireland for most of it.

Basically is it 5 years exactly from my date of arrival, or 5 full calendar years ignoring the one when I arrived, or will they really credit me for time I didn't spend in the country?

5 years from date of arrival.