Soulwise
Bayesian Cycle Prediction
Astrology content is for reflection and entertainment, not medical, financial, legal, or mental-health advice.
What is Bayesian cycle prediction?
A statistical method that estimates where you are in your cycle-related cycle by combining a prior your historical cycle length with new evidence each daily check-in . Soulwise uses it instead of fixed 28-day assumptions so the phase read improves as you log more days.
- Prior = your own past cycles, not a 28-day default
- Updates with each daily check-in
- Reports uncertainty honestly — no false precision
Bayesian Cycle Prediction
Most cycle apps default to a 28-day assumption and either ignore variance or correct after the fact. Soulwise uses Bayesian prediction instead — a statistical approach where the estimate of "what phase are you in today" is the posterior of two things: your historical cycle length (the prior) and the daily check-ins you have logged this cycle (the evidence).
Why Bayesian, not fixed
A fixed 28-day cycle is confidently wrong for most people. The practical normal range is 21 to 35 days, individual variance month-to-month is large, and life events (stress, travel, sleep, training load) shift cycle length more than most people expect. A fixed-length estimator gives you a precise phase label when the underlying uncertainty is high.
Bayesian estimation gives you a phase label with an uncertainty band. When the band is wide (early in your data, or after a cycle that ran long), Soulwise says so on the phase card. When the band is narrow (after several stable cycles), the phase label is trustworthy.
What goes into the prior
- Your last six cycles' lengths, if available.
- A weakly-informative starting prior (28 ± 5) before any data exists.
- A drift term so older cycles weigh less than recent ones.
What goes into the evidence
- Your daily check-in chips and energy slider.
- Any logged bleed or spot.
- Optional experiences marks (header, cramp) if you log them.
The system does not use:
- Basal body temperature (we are not a fertility tracker).
- experiences-based ovulation guesses (out of scope).
- Cervical mucus reports (out of scope).
What it does not do
It does not predict ovulation for contraception or conception. See non-wellness-cycle-tracking for the full anti-claim posture.
It does not give a single-day pinpoint when uncertainty is high. The phase card shows a 2- to 4-day window with confidence shading.
It does not learn from anyone else's data. Each user has their own Bayesian model, run on-device, against their own encrypted history.
Where it shows up
In the phase card in the daily ritual, in the recap letter, and as the input to cycle-weather — the short-term variance read compared to your stable baseline.
Related Content
Go deeper
See Bayesian Cycle Prediction read in your full birth chart
A free placement is the headline. A full reading interprets your whole chart.
Frequently Asked Questions
Because most cycles are not 28 days. Anything from 21 to 35 days is normal, and individual variance month-to-month is large. A fixed assumption gives confidently wrong predictions.
No. Soulwise is non-wellness. It estimates which phase you are in for the daily ritual context — it does not predict ovulation for fertility or contraception.
Accuracy improves with data. After three cycles, phase estimates are usable for the daily ritual; after six cycles they are stable. Soulwise reports its own uncertainty in the phase card.