Vocabulary retention estimate calculator

Calculate fitted day-zero recall fraction and fitted log-decay slope with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use fitted day-zero recall fraction and fitted log-decay slope to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

Observed tests JSON [days since study,recall fraction]
[[0,0.8],[10,0.4],[20,0.2]]
Forecast day since study (days)
30
Fitted day-zero recall fraction
0.8
Fitted log-decay slope (per day)
-0.069315
Raw fitted forecast recall fraction
0.1
Fitted half-life (days)
10

Try another scenario

Observed tests JSON [days since study,recall fraction]
[[0,0.8],[10,0.4],[20,0.2]]
Forecast day since study (days)
40
Fitted day-zero recall fraction
0.8
Fitted log-decay slope (per day)
-0.069315
Raw fitted forecast recall fraction
0.05
Fitted half-life (days)
10
Calculation method

Calculation method

Fitted day-zero recall fraction

A=exp(OLS intercept of log(recall) versus day).

Fitted log-decay slope (per day)

OLS slope on log(recall).

Raw fitted forecast recall fraction

A*exp(slope*forecastDay), with out-of-range values explicitly flagged by UI.

Fitted half-life (days)

-ln(2)/slope when slope<0; else No decreasing half-life.

Symbols and units
a
Observed tests JSON [days since study,recall fraction]
b
Forecast day since study (days)

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Assumptions & limits

Assumptions & limits

  • Descriptive log-linear fit only, not a validated memory law. Does not account for review, testing effects or heterogeneous words; forecast uncertainty is not quantified. Display warning if fitted recall outside [0,1]. Supported limits: 2..100 tests; unique days>=0; recall in (0,1]; forecastDay>=0; finite exponential result.
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Further reading

Method reference ↗

Background reading; this does not imply endorsement or independent review of SumFizz.

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