Reckonable residence refers to the time in Ireland that counts towards eligibility for citizenship by naturalisation.
The total time when applying through naturalisation is 1825 days or at least five years within eight years of living in Ireland. If you are applying as a spouse or civil partner of an Irish citizen, reckonable residence is 1095 days or at least three years within five years of living in Ireland.
When applying for citizenship, you must prove you spent that time in Ireland through your visa stamps. Not all stamps count. Those that count include:
Stamp 1
Stamp 1G (if you are the spouse/civil partner/de facto partner)
Stamp 3
Stamp 4
Stamp 5
If you held Stamp 1G as a graduate student, your time doesn’t count. Also, the time you spent in Ireland with stamp 0, Stamp 1A, Stamp 2, or Stamp 2A does not count towards reckonable residence.