This article makes a serious andscientific attempt to develop appropriate fonnulae and to apply them for finding out the students'pass out rates for different academic years of different programmes of IGNOU. The minimum and maximum durations prescribed for completion of different programmes vary widely. Sequel to it, the students admitted to a programme in different academic years will be completing the minimum and maximum durations in different years. The students ,admitted to a programme may therefore pass it out in any year between the respective minimum and maximum durations and the pass outs are accordingly spread over different years. Once the first batch of students of a programme completes minimum duration, the students start passing out every year till the completion of maximum duration by that batch. Meanwhile, the students from successive batches of that very programme also complete the minimum duration and start passing out every year. Thus, the pass outs of a given programme of a given year include the pass outs from students admitted in different academic years. The cohort of students on rolls forming a base group for the pass outs of every year are also spread over a few years. For arriving at the figures of cohort of students on rolls in every successive year, the number of students who have already passed out in the previous year(s) should be deducted from the enrolment of respective year(s), and wherever applicable the remaining students of particular batch(es) who have completed the maximum duration of the programme should also be deducted from the cumulative enrolment of cohort years. Because of these complications linked to the flexibility in duration allowed for completion of the programmes, calculating the students pass rates for different academic years of different programmes has been a difficult task, which the author accomplishes in this article.