Deterministic and versioned, logged every time it runs — never a model, never an AI-generated figure.
- Take your income and spend for each of the last 3–6 calendar months with real transaction history (a month before your first connected account isn't counted as a zero-income month — it's excluded as no data).
- Projected income and spend are the median of those months — less swayed by one unusually large or small month than an average would be.
- Commitments are your active recurring obligations (Commitments page), converted to a monthly-equivalent figure (a quarterly premium counts as one-third a month, an annual one as one-twelfth).
- Projected surplus = median income − median spend − monthly commitments. The range around it is a median-absolute-deviation band from your own income and spend history, widening with the square root of how many months ahead the projection reaches — the same "uncertainty compounds with distance" shape the rate forecast uses.
Affordability check. In the last three days of each month, if next month's pessimistic-case surplus plus your liquid balance would still be negative, you get a notification naming the shortfall — before the month starts, not after a payment fails.
Fewer than 3 months of real history yields no forecast at all, rather than a range built on too little data. This is illustrative information, not financial advice.