If you miss the deadline for presenting theSpanish tax return you risk fines and other additional costs on top of the tax owed.
Below is a guide to late submission and non payment fines and uinterest charges. This is just a guideline as each case is judged individually and there are sometimes reductions for timely payment of the fine.
Late presentation fine:
Up to 3 months of due date 5% of tax due
Between 3-6 months 10%
Between 6-12 months 15%
More than a year overdue 20%
Interest at 5% is charged on top for payments more than 1 year late
Fines for late submission of a nil return where no tax is due: €100 (€200 if the Tax Office has prompted the tax payer to make a return)
Extra Penalties payable if a late submission is not made voluntarily (ie the tax office has to chase the payer)
Minor infraction 50% of tax + fine + interest
Serious infraction 50-100% of tax + fine + interest
Very serious infraction 100-150% of tax + fine + interest
The lowest penalty is applied if the taxpayer has not deliberately tried to hide the income and if the amount of the tax and fines is less than 3.000€. The penalties for serious infractions apply when forged documents are discovered, fraudulent intentional under declarations have taken place, or there have been repeated infractions after previous warnings.
The Spanish tax office can go back 4 tax years which in real terms is 5 years and 3 months from the end of a tax year.
I believe that at the very least it makes sense to clarify what your tax liability is, and if at all possible keep things up to date, rather than looking over your shoulder and waiting for a fine to drop on the mat, or worse still miss a registered letter because you are not in Tenerife all the year and suddenly find amounts garnered from your Spanish bank account.