Alimony payments tend to be set as a fixed amount to be revised annually based on how much the Consumer Price Index (CPI) has risen.
The CPI rose by 1.2% between December 2017 and 2018. This means that in January 2019 alimony payments should increase proportionately.
For example, if monthly alimony of €200 was settled:
€200 x 1.2% = €2.40
€200 + €2.40 = €202.40
As from January, monthly alimony should therefore be €202.40.
If the annual revision is carried out at any time during the year other than January, the increase can be calculated on the INE (National Statistics Institute) website: https://www.ine.es/varipc/index.do