The TAE (Spain's equivalent of the APR, Annual Percentage Rate) is the indicator that truly allows you to compare financial products with one another, because unlike the TIN (nominal rate), it includes fees, expenses, and the effect of how often interest compounds.
Why it matters
Two loans with the same TIN can have different TAEs if one charges higher arrangement or processing fees. By law, all institutions in Spain must display the TAE in advertising and in the binding offer, precisely to make comparison easier.
The TAE isn't the total cost
The TAE is an annualized percentage, not the total amount you'll pay. For very long-term mortgages or ones with very high upfront fees, it's also worth looking at the total cost of the credit (TIN + fees + required insurance), not just the TAE.
Rule of thumb: to compare two mortgage or loan offers, always look at the TAE, not the TIN.