What is time to fill?
Time to fill is a recruiting metric: the number of days from when a job opening is opened, either at requisition approval or at posting, to when a candidate accepts the offer. Companies define the start point differently, so state which one you use whenever you report it.
Common formula
A common industry definition is: time to fill = date the offer is accepted minus date the requisition was opened (or the job was posted). For an average, add the days for each filled role and divide by the number of roles filled. Define in advance how you treat roles that were put on hold or canceled.
Time to fill versus time to hire
Time to fill usually starts when the role opens and measures the whole process from the employer's side. Time to hire usually starts when the candidate applies or is first contacted and measures the candidate's experience. Track both only if you label them clearly.
Example
A requisition is approved on day 1 and the chosen candidate accepts the offer on day 46. Time to fill for that role is 45 days.