Good question. It depends.
Time since surgery is the most consistently used criteria. It is also the most misleading indicator. The calendar never knows when you are ready. Most people are told that it will take 1 year, but that is often under an ideal scenario. That scenario requires consistent adherence to your rehab program, regular checks of your progress and a long term commitment of effort, time, and money. Inevitably, many will drop off the program along the way.
Re-injury rates remain high following ACL surgery. Often because of incomplete rehab and because there are not clear, established benchmarks that determine success. Also, many people who suffer an ACL tear will never actually return to their previous level of activity. It is an area of big concern for many medical professionals.
Rehab professionals use a combination of factors to look at readiness to return—strength tests, functional tests (most often hopping and jumping) as well as survey information to see how good you feel about your knee. A study by JOSPT underscores how difficult the decision can be.
If the survey revealed you did not feel confident in your knee, you would most likely not pass the other tests and not be ready. However, even if you felt good about your surgery about 50% of the time you overestimated your ability and would still not be ready.
PT’s also know that just having good strength in your leg or being able to pass the hopping tests is often not sufficient to return to the field. A movement analysis is highly recommended in addition to other testing to give an objective measure of how confident you are in your leg. Can you change direction symmetrically? Can you absorb shock and generate power in the limb without making compensations? It helps determine quality not just quantity of movement.
There still is no simple benchmark to determine when you are ready to play. You need to complete all basic rehabilitation, you need to have good strength in the leg. You need to feel confident in the leg and you need to be able to pass a movement test. Most people that have ACL surgery cannot check all those boxes and most do not return to their sport.
The best news is that the calendar never knows when you are ready to return, but it also does not determine when you have failed to return. I have seen many clients pick up their sport after years away. There is no substitute for strengthening and movement training to regain confidence in your knee. All it takes to get started is a couple more clicks.