The relevant info is the amount of interest you are paying, the number of years into your mortgage you are and how many people are on the mortgage.
If you're in years 1 or 2, the relief is 25%
If you're in years 3, 4 or 5 the relief is 22.5%
If you're in years 6 or 7 the relief is 20%
This relief is applied to interest paid up to a ceiling of €10,000 for a single applicant or €20,000 for a couple (so if you are paying €10,000 interest in year 3 of your mortgage, your TRS will be €2250 p.a. or €187.50 per month)
After the first 7 years, TRS is 15% on interest up to a ceiling of €3000 (so €450 TRS p.a. max)