Plan ahead

Goal: know whether the money lasts, and when it would run out, before it does.

Tools: forecast_balance, then set_category_budget. Prompt: plan_next_month.

The conversation

1. Ask, with what you know.

   You: If I earn 3,200 a month, will my accounts go below zero before the end of the year?

2. The agent projects. forecast_balance with {"until": "2026-12", "monthly_income": 3200} — two YNAB requests:

   forecast_balance (excerpt)

   {
     "message": "The balance stays above zero until 2026-12. This rests on the assumptions listed: check them with the user.",
     "accounts": [
       "Checking",
       "Savings"
     ],
     "start_balance": 4112.66,
     "assumptions": {
       "recurring": [
         {
           "payee": "MARKET FRESH",
           "amount": -182.58,
           "day": 14,
           "months_seen": 3
         },
         {
           "payee": "RAIL CO",
           "amount": -45.0,
           "day": 18,
           "months_seen": 3
         },
         {
           "payee": "STREAMFLIX",
           "amount": -13.49,
           "day": 15,
           "months_seen": 3
         },
         {
           "payee": "TENNIS CLUB - PRELEV",
           "amount": -22.0,
           "day": 20,
           "months_seen": 3
         }
       ],
       "variable_monthly": -68.7,
       "monthly_income": 3200.0,
       "one_offs": [],
       "scheduled": [
         {
           "scheduled_id": "sch-rent",
           "date": "2026-10-03",
           "amount": -950.0,
           "account": "Checking",
           "category": "Rent",
           "payee": "LANDLORD SARL",
           "memo": null,
           "frequency": "monthly",
           "transfer": false
         },
         {
           "scheduled_id": "sch-phone",
           "date": "2026-10-08",
           "amount": -19.99,
           "account": "Checking",
           "category": "Phone",
           "payee": "TELCO MOBILE - PRELEV",
           "memo": null,
           "frequency": "monthly",
           "transfer": false
         },
         {
           "scheduled_id": "sch-power",
           "date": "2026-10-12",
           "amount": -64.2,
           "account": "Checking",
           "category": "Electricity",
           "payee": "POWERCO ENERGIE",
           "memo": null,
           "frequency": "monthly",
           "transfer": false
         },
         {
           "scheduled_id": "sch-insurance",
           "date": "2026-10-20",
           "amount": -420.0,
           "account": "Checking",
           "category": null,
           "payee": "HOMESAFE INSURANCE",
           "memo": null,
           "frequency": "yearly",
           "transfer": false
         },
         {
           "scheduled_id": "sch-rent",
           "date": "2026-11-03",
           "amount": -950.0,
           "account": "Checking",
           "category": "Rent",
           "payee": "LANDLORD SARL",
           "memo": null,
           "frequency": "monthly",
           "transfer": false
         },
         {
           "scheduled_id": "sch-phone",
           "date": "2026-11-08",
           "amount": -19.99,
           "account": "Checking",
           "category": "Phone",
           "payee": "TELCO MOBILE - PRELEV",
           "memo": null,
           "frequency": "monthly",
           "transfer": false
         },
         "… 4 more"
       ]
     },
     "months": [
       {
         "month": "2026-09",
         "start": 4112.66,
         "inflows": 3200.0,
         "outflows": 0.0,
         "end": 7312.66,
         "lowest": 4112.66
       },
       {
         "month": "2026-10",
         "start": 7312.66,
         "inflows": 3200.0,
         "outflows": -1785.96,
         "end": 8726.7,
         "lowest": 6665.72
       },
       {
         "month": "2026-11",
         "start": 8726.7,
         "inflows": 3200.0,
         "outflows": -1365.96,
         "end": 10560.74,
         "lowest": 8089.84
       },
       {
         "month": "2026-12",
         "start": 10560.74,
         "inflows": 3200.0,
         "outflows": -1365.96,
         "end": 12394.78,
         "lowest": 9913.8
       }
     ],
     "first_shortfall": null
   }

3. The agent reads the assumptions to you before the conclusion:

   Claude: Starting from 4,112.66 across Checking and Savings, with 3,200 a month in, your recurring charges (rent 950, groceries about 182.58, electricity 64.20, the train 45, tennis 22, phone 19.99, Streamflix 13.49) and about 69 of other spending, the balance keeps growing: the lowest point, 4,112.66, is today. Anything coming I should add?

4. You correct. Add what the history cannot know:

   You: The property tax, 1,426, on 15 October.

   The agent calls again with one_offs: [{"date": "2026-10-15", "amount": -1426, "label": "property tax"}].

What the projection assumes

Assumption	Where it comes from	Change it with
Starting balance	today’s balance of the open on-budget accounts	account_ids
Recurring charges and income	the same payee in 3 of the last 4 full months, each month within 20 % of its median	— (returned in assumptions.recurring)
Other spending	average of the last 3 full months, recurring charges excluded	variable_monthly
Income	what you give; otherwise the last 3 months’ average	monthly_income
One-off amounts	only what you give	one_offs

Details: Forecasting.

Reading the answer

• months[].start, inflows, outflows, end: the month’s balance and flows.
• months[].lowest: the lowest point within the month, day by day — the one that tells you whether a payment would bounce.
• first_shortfall: the first month whose lowest point is below zero, or null.

A projection, not a prediction

It extends your recent months. A holiday, a yearly tax or a one-off purchase in them pushes the averages; a new expense is invisible until you add it. Read the assumptions before the conclusion.

Then budget next month

You: Prepare October’s budget from this.

The agent proposes next month’s amounts category by category — recurring charges first, then the rest from recent spending — and applies those you accept with set_category_budget, one previewed change each.