How many passes does Defrag take in Windows 10?

Disk Defragmenter might take from several minutes to a few hours to finish, depending on the size and degree of fragmentation of your hard disk. You can still use your computer during the defragmentation process.

Microsoft never specifically says, because Windows auto-detects the needed settings. The amount and time is different for every situation.

Windows 8 and up auto-detects the number of passes required depending on the SMART status, number of errors, size of disk, time since last inspection, etc. You can keep it running in background and does not affect your performance much on a decently speced device. It can take anywhere from 1-2 passes to 40 passes and more to complete. There is no set amount of defrag. You can also manually set the passes required if you use third party tools. Ho much fragmented was your drive?

Took me about 14 hours, at least 4 passes (each subsequent pass was significantly faster, might've been more than 4 passes but if so I missed seeing any passes above the 4th).

(1TB HDD, Windows 10, i5-8250U, laptop about 4 years old)