What it is and who it makes sense for
It is a temporary policy — from one day to a few months — for vehicles that do not run all year: the inherited car that needs moving, the motorbike that only comes out in summer, a one-off transfer or the newly bought car you have not yet insured.
Remember: in Spain a vehicle cannot be driven or even parked on a public road without insurance. That is also what the DGT's temporary deregistration (baja temporal) is for — the free alternative if the car will sit in a garage.
How much it costs
Considerably more expensive per day than an annual policy — a single day can cost as much as weeks of a normal policy — but far cheaper than insuring a car for a whole year when you will use it for two weeks. The maths is quick: past a certain number of days per year, the annual policy wins.
Alternatives that sometimes work out better
If you are going to drive someone else's car for a few days, it is often enough that their policy allows authorised drivers — many policies cover any driver over a certain age. And if it is your second, seasonal-use vehicle, some insurers offer annual policies with temporary suspension that end up costing less than buying cover by the day.
Every case has a different solution — tell us yours and we will tell you the cheapest one, with no obligation.