At the meeting on Friday, the lady from SUMA talked about the rateable value of property and how this affected the tax that you pay. She explained that the catastral value was increased to reflect market values. Up to 2005 the increase factor was 1.020 year on year.
So if you look at last year's bill and find Base Liquidable then multiply it by this factor you should get a rough value for this year's bill.
Once you have determined the new Base Liquidable then you can use SUMA's calculator at their website http://www.suma.es/ to calculate the tax you will pay. The factor for Bigastro for 2008 is 0.68% as set out in the ORDENANZA SOBRE BIENES INMUEBLES.
If you want to view the details that Cadastro have for your property you can do so by going to the Catastro Virtual Office:-
If you know the reference number for your property then you can type it in otherwise:- Select the province, the town, the road type, road name and number of your house to bring up details including diagrams of your plot.
Whilst you are at the SUMA site; you can work out your car tax as well. You select BIGASTRO as the town and then type in the Potencia fiscal which you'll find on your Tarjeta Inspección Téchnica de Vehículos (remembering to use a comma rather than a decimal point where necessary).
Of course you will have already know what it is for this year but at least you now know how to work out next year's bill before it arrives.