Spanish Vocabulary Retention Estimator
Estimate long-term Spanish vocabulary retention using the Ebbinghaus Forgetting Curve combined with spaced repetition and active recall factors.
Number of Spanish words you have actively studied.
How many days ago you last reviewed the vocabulary.
Total number of times you have reviewed this vocabulary set.
Your average correct recall rate during practice sessions (1–100%).
Your primary method of studying Spanish vocabulary.
Sleep strongly affects memory consolidation.
Your results will appear here.
Formula
1. Memory Stability (S):
S_base = (1 + 0.5 × reviews)^0.6
S_adjusted = S_base × (0.5 + recallAccuracy)
S_final = S_adjusted × methodFactor
2. Sleep Consolidation Factor:
sleepFactor = min(0.7 + 0.3 × (sleep / 8), 1.0)
3. Ebbinghaus Retention Rate (R):
R = e^(−daysSinceReview / S_final) × sleepFactor
4. Words Retained:
wordsRetained = totalWords × R
5. Next Optimal Review Interval (90% threshold):
nextReview = S_final × ln(1/0.9) ≈ S_final × 0.10536
Assumptions & References
- Ebbinghaus Forgetting Curve (1885): Retention decays exponentially as R = e^(−t/S), where t is elapsed time and S is memory stability.
- Memory Stability Growth: Based on SuperMemo SM-2 algorithm principles — each successful review increases the interval before the next review is needed.
- Recall Accuracy: Higher active recall accuracy during practice is associated with stronger memory traces and slower forgetting (Roediger & Karpicke, 2006 — "The Testing Effect").
- Study Method Multipliers: Passive reading offers the least durable encoding; SRS with immersion provides the strongest consolidation (Cepeda et al., 2006).
- Sleep & Memory Consolidation: Sleep, especially 7–9 hours, is critical for hippocampal-to-cortical memory transfer (Walker, 2017 — Why We Sleep). Below 7 hours reduces consolidation efficiency.
- Optimal Review Threshold: Set at 90% retention — the point at which reviewing is most efficient for long-term learning (Pimsleur, 1967; Wozniak & Gorzelanczyk, 1994).
- This estimator provides an approximation. Individual variation in memory, word complexity, and prior language exposure will affect actual results.