Every deductible expense lowers your net business income, and with it two things at once: your IRPF and, beyond a point, your cuota bracket.
Requirements for an expense
It must be linked to your activity.
It must be backed by an invoice in your name.
It must be recorded in your expense book.
Common expenses
The cuota de autónomos itself.
Your gestoría, advisers and invoicing software.
Materials and equipment: items over €300 are depreciated over several years.
Utilities if you work from home: 30% of the share matching the floor area you use for work.
Health insurance: up to €500 a year per person (you, your partner and children under 25).
Training related to your activity, professional association fees, advertising and office rent.
Meals on working days away, within the daily limits set by the tax office and paid electronically.
The 5% that needs no invoice
In the simplified regime you can also deduct 5% for hard-to-justify expenses, up to €2,000 a year. The calculator applies it automatically.
How much you save
An expense is not free: it cuts your taxes at your marginal rate, not by 100%. If your marginal rate is 30%, a €1,000 expense saves you about €300 of IRPF. If it also drops you a cuota bracket, you save on Social Security too.
Try entering your yearly expenses in the calculator and compare your net with and without them.