Retention Decay Check Calculator

📖 Overview

Learning fades even after strong first comprehension.

This calculator projects remaining retention from initial mastery and daily decay assumptions.

Use it to schedule refresh sessions before forgetting crosses critical threshold.

Use these default and higher-pressure example inputs to explore how sensitive this calculator is before using your real numbers.

Estimates memory decline over time with a daily exponential decay model for review planning.

The Formula

Current Retention = Initial Retention × (1 − Daily Decay Rate)^Days

Initial Retention	Estimated mastery immediately after learning/review
Daily Decay	Average daily forgetting rate assumption
Days	Time since last substantial revision session
Current Retention	Estimated retained knowledge now

💡This model helps timing decisions for spaced repetition; it is a planning approximation, not a neurological measurement.

Initial	Decay/day	10 days	20 days
90%	1%	81.4%	73.6%
90%	2%	73.5%	60.1%
95%	2.5%	73.3%	56.6%
85%	3%	62.7%	46.2%

Use this tool when you need a fast decision during active planning or execution.
Use this before committing money, time, or tradeoffs that are hard to reverse.
Use this to compare options using the same assumptions across scenarios.

Results can be misleading if key inputs are missing, stale, or unrealistic.
Very small or very large values may amplify rounding effects and interpretation risk.
If assumptions change mid-decision, recalculate before acting.

💡 Use this to trigger spaced review before retention drops too far.

💡 Higher initial retention does not eliminate decay pressure.

💡 Tune decay rate from your own recall-test history for better accuracy.

❓ Is daily decay constant in real life?

No, but a constant-rate model is useful for planning.

❓ Can retention go below zero?

No, the model asymptotically approaches zero.