The January-to-May problem
Class 11 typically ends in December or January. JEE Main Session 1 is in late January; Session 2 is in April. A student finishing the syllabus in November and sitting Session 2 in April has let early Class 11 chapters — Trigonometry, Sequences and Series, Units and Dimensions, Basic Organic Chemistry — go cold for 90 to 120 days.
That is not a scheduling inconvenience. That is a near-certainty of significant forgetting.
What the forgetting curve actually does
Hermann Ebbinghaus quantified memory decay in the 1880s. The core finding: without active recall, retention follows a decay curve that drops fastest in the first 24–72 hours and slows as time passes. Most people retain only 30–40% of new material after a month without review.
For a JEE aspirant, the practical implication is concrete. A concept learned in August and not actively revisited since December will feel unfamiliar in April — not impossible to recall, but effortful, and under timed exam conditions, effortful is the same as slow, which is the same as wrong.
The key variable is not how long ago you learned something. It is how many times you have successfully retrieved it since. Each successful active recall — attempting the problem, retrieving the method, getting it right — resets the decay clock and flattens the curve for that concept. A concept you have recalled three times, spaced out over several weeks, retains far more durably than one you studied for three hours in a single session.
Why "I'll revise in April" doesn't work
April is not a good time to re-learn Class 11 Trigonometry. Re-learning a faded chapter — rebuilding the concept from near-zero — costs roughly the same time as learning it the first time. Scheduled revision of a partially-retained chapter costs a fraction of that.
Students who defer all Class 11 revision to April are not revising. They are re-studying. The time budget in April does not accommodate this. April is for full-length mocks, for speed, for exam temperament. April is not for encountering the Sine Rule for the second time ever.
The cost is not abstract. A student who needs to re-study three Class 11 Physics chapters in April is spending time that should have gone to mock analysis and weak-area refinement. They enter the exam with less practice time, not less content — and that is a harder deficit to recover from.
How Rhovecs handles per-concept decay
We compute a per-concept forgetting risk score from two signals: mastery score (how reliably you solved this concept's structural variants) and stability score (how long since you last demonstrated that mastery at full difficulty). These combine into a time-weighted decay estimate for each concept in your syllabus.
When a concept's predicted retention drops below our threshold — before you forget it, not after — it is automatically added to Today's Focus as a short review drill. You solve two or three problems. That is enough to demonstrate active recall, which resets the decay clock. The concept recedes from the queue. If it decays again in three or four weeks, it returns.
You do not plan the revision schedule. You do not maintain a spreadsheet of last-revised dates. The engine does this for every concept, in every subject, simultaneously.
Class 11 Trigonometry in April should feel warm. If it feels cold, the revision scheduling failed. Ours is designed so it doesn't.