After a few weeks with the spaced repetition system, the question that kept nagging me was whether I could already start learning a new group of words, or should I keep repeating the current ones.

I needed a decision rule.

So after a discussion with Claude Code I decided to introduce an overdue score. Now a new group is added to the pack only if nothing is in the overdue list.

What I saw was not great — it turns out I have 17 (!) groups overdue at the time of this writing. These are top 10 items:

How the overdue score works

Each time I complete a full session on a group, the next review is scheduled further out. The interval doubles with every session: interval = 2^(sessions−1) days. First review after 1 day, second after 2, third after 4. By the tenth session, the system expects me to remember the group for over a year without review.

The interval also adjusts based on hint usage. The more hints I needed in a session, the shorter the next interval — the system schedules that group back sooner without me having to rate anything.

The overdue score is elapsed / effective_interval. Below 1 — still on track. Above 1 — overdue. The group score is the worst of the two types: if pinyin is fine but strokes are overdue, the group is overdue.

Stroke and pinyin are scheduled independently

Each group has two independent schedules — one for stroke, one for pinyin. Completing a pinyin session does not affect the stroke schedule. A group can be current on pinyin and three days overdue on strokes at the same time.

You can't offset a stroke debt by drilling pinyin. The system tracks each separately.

The rule: catch up before moving on

A new group enters only when every active group has an overdue score below 1 — both stroke and pinyin. If anything is overdue, catch up first.

Spaced repetition only works if you show up for the reviews. Adding new material while old material decays defeats the purpose.

Stay tuned for more updates on how the system evolves.