The JSS 24-month window is the span of contract history, the most recent two years, that Upwork counts when it calculates a freelancer's or agency's Job Success Score.
Upwork's Help Center states that the Job Success Score is based on the past 24 months of activity. The window rolls forward with every fortnightly update, so a contract that ended two years ago drops out at the next review and a new one enters as soon as it closes. The score at any moment is therefore a statement about the last two years, not a lifetime record, and the work history going back further on the profile has no bearing on it.
Three consequences follow. A contract that ended badly weighs on the score for up to two years and then disappears from it entirely, which is why a profile can recover without any new work. A profile that stops taking contracts keeps its score for a while and then loses it, because the window empties; an absent score usually means inactivity, not poor work. And a new profile has no score until enough contracts have closed inside the window, which Upwork distinguishes from a low score.
Upwork has changed how it describes the window over the years, and it may do so again. The 24-month figure is the current published one; whether Upwork also looks at shorter spans internally is not something it discloses.
How Upwork Insights uses it
The index records the score as the public page shows it at observation time, with no attempt to reconstruct the window. Among the 28,921 agencies indexed as of Oct 31, 2026 the median score of rated agencies is 100%, and the ranking can be sorted by JSS. In the Index Score the JSS is the quality component, 20 of 100 points, with unrated agencies at half.