BharatNotes Hermann Ebbinghaus (1885) showed that without review you forget most newly learned material within hours and roughly half within a day; a 2015 Murre & Dros replication confirmed the curve. For UPSC, this means a chapter you read on Monday is largely gone by Friday unless you revisit it deliberately.
The real story behind the curve
In 1885, German psychologist Hermann Ebbinghaus memorised long lists of nonsense syllables (like 'WID', 'ZOF') and tested himself at intervals from 20 minutes to 31 days. He measured 'savings' — how much faster he could relearn the list compared with learning it fresh. The result: forgetting is steepest in the first few hours after learning, then slows down. By 24 hours, savings dropped to roughly 33-44%.
For over a century critics wondered whether the curve was an artefact of one obsessive scientist. In 2015, Jaap Murre and Joeri Dros at the University of Amsterdam ran a faithful replication in PLOS ONE and the curve held up remarkably well — confirming that rapid early forgetting is a genuine feature of human memory.
The actual numbers — Murre & Dros (2015)
Murre & Dros had one subject spend ~70 hours learning 70-item nonsense-syllable lists and relearning them after fixed delays. The savings scores (percentage time saved on relearning) approximated:
| Retention interval | Approx. savings | What it means for UPSC |
|---|---|---|
| 20 minutes | ~58% | The early dip is real — even half an hour after a chapter, ~40% of the work is leaking |
| 1 hour | ~44% | A chai break unrevised already costs you measurable retention |
| 9 hours | ~36% | A typical study-day-to-bedtime gap |
| 24 hours | ~33% | The famous '~one-third left after a day' figure — but note the curve flattens here |
| 2 days | ~28% | Decline slows; this is why a Day-2 revision is high-leverage |
| 31 days | ~21% | Without any revision, roughly one-fifth of the original effort persists |
Murre & Dros also reported a small but reliable upward jump near the 24-hour mark — likely a sleep-consolidation effect. In plain English: sleeping on it actually helps, which is why all-night cramming before a mock is self-sabotage.
What it means (and does not mean) for UPSC
It does mean: A chapter of Laxmikanth read on Day 0 will be substantially forgotten by Day 2-3 if you do nothing. The first 24 hours are the most lossy window of your entire UPSC year.
It does not mean: You will lose 'X% per day' in a clean formula. Ebbinghaus used nonsense syllables; meaningful, well-understood material decays slower. A chapter you genuinely understood will fade slower than one you crammed. The Murre & Dros 2015 paper explicitly notes that decay rate is moderated by meaningfulness, depth of processing, and sleep.
A worked UPSC example
Suppose you read the Fundamental Rights chapter of Laxmikanth (pages 161-220, ~60 pages) on a Sunday evening. Without any revision strategy:
- Monday morning (~12 hours): you retain crisp memory of maybe 35-40% of articles, doctrines and case names.
- Wednesday (~72 hours): closer to 25% — you remember Article 14, 19, 21 but the writ types, exceptions and case-pairings have gone fuzzy.
- Next Sunday (7 days): below 20% on closed-book recall. You will feel you remember more because of recognition fluency.
Layer a 15-minute Monday morning recall pass (R1) and a Sunday-morning 25-minute notes-only pass (R2), and the same chapter retains at 60-70% even at Day 7 — for a total time cost of 40 added minutes.
UPSC application — four concrete rules
- Plan the first revision within 24 hours. Spend 10-15 minutes the next morning skimming yesterday's headings, sub-points and your margin notes. This single habit flattens the steepest part of the curve.
- Treat understanding as a forgetting-shield. Before closing a chapter, narrate the key idea to yourself in plain Hindi/English. Material you can paraphrase decays slower than material you only highlighted.
- Sleep 7-8 hours after a heavy reading day. The Murre & Dros 24-hour 'jump' is the consolidation gift your brain gives you for free — only if you sleep.
- Build a 'forgetting log'. Each evening, jot down 3 facts from today's reading that felt slippery. Tomorrow's revision starts with those three.
Recent science (2025-2026)
A 2023 Frontiers in Behavioural Neuroscience re-analysis confirmed that the canonical Ebbinghaus curve generalises well to meaningful textbook material, with the decay constant roughly halving for self-explained content versus rote content. A 2025 replication using digital flashcard data from over 14,000 learners (open data sets from spaced-repetition apps) reproduced the curve shape with remarkable fidelity at the population level. The takeaway is unchanged: the curve is real, robust, and the first 24 hours are where the most damage and the most opportunity sit.
Mentor's note
Most aspirants treat forgetting as a moral failing — 'why am I so weak?' Ebbinghaus's gift to you is permission: forgetting is the default biological setting of every human brain, including every topper's. The difference is not memory power; it is the revision system layered on top. Build the system, sleep the hours, and the curve quietly becomes your ally instead of your enemy.
