Can I claim business mileage without a logbook?

Usually, no—not if you mean a mileage deduction based on business use of a vehicle. Tax authorities generally expect a contemporaneous mileage log or another contemporaneous record that shows the business purpose, date, destination, and miles traveled.

That said, if you did not keep a formal logbook, you may still be able to reconstruct your mileage later using other records such as calendars, appointment records, emails, invoices, odometer readings, service records, or GPS/location history. Whether that reconstruction is accepted depends on your tax jurisdiction and how complete and credible the records are.

If your proof is weak, the deduction can be reduced or denied, and penalties or interest may apply. Because the exact rules vary by country and sometimes by state or business type, check the official guidance for your area or ask a tax professional before claiming it.