Vocabulary Retention Calculator
Spaced-repetition words retained over time.
Enter your values
Enter the new words per day you are working with.
Enter the days studied you are working with.
Enter the reviews per word you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Words retained
- 360
- Words introduced
- 900
- Retention rate
- 40%
- Memory strength (days)
- 27.6
Quick answer
Retention decays exponentially, and each review resets the curve to a slower decay.
Retained = new × e^(−days ÷ strength)
At a glance
| What it does | Spaced-repetition words retained over time. |
|---|---|
| Category | Education |
| Inputs needed | New words per day, Days studied, Reviews per word |
| Main output | Words retained |
| Formula | Retained = new × e^(−days ÷ strength) |
| Cost | Free — no sign-up, no download |
How to use the Vocabulary Retention Calculator
- 1Enter how many new words you add each day.
- 2Enter how long you have been studying.
- 3Enter typical reviews per word.
Inputs explained
- New words per day
- Enter the new words per day you are working with.
- Days studied
- Enter the days studied you are working with.
- Reviews per word
- Enter the reviews per word you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- New words per day15
- Days studied60
- Reviews per word4
Results
- Words retained360
- Words introduced900
- Retention rate40%
- Memory strength (days)27.6
Frequently asked questions
Why do reviews matter so much?
Each successful recall lengthens the interval before you forget.
Is this exact?
No — it models Ebbinghaus's curve to show trends, not guarantees.
What do I need to enter into the Vocabulary Retention Calculator?
Just 3 values: new words per day, days studied, reviews per word. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Vocabulary Retention Calculator work out the answer?
Retention decays exponentially, and each review resets the curve to a slower decay. It applies the formula Retained = new × e^(−days ÷ strength) and shows the working so you can check each step by hand.
Is the Vocabulary Retention Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.