A budget says where money should go. A cash-flow forecast says whether the checking account survives the next 13 weeks given real paycheck dates and real due dates. Households bounce checks in rich months when rent, insurance, and a car payment land before the deposit clears.
This guide builds a lightweight 90-day forecast you can keep in a spreadsheet or notebook. It pairs with Budgeting basics and stays separate from a quarterly wealth snapshot (Net worth vs cash flow).
What you need on one page
| Input | Where to get it |
|---|---|
| Pay dates and net amounts | Pay stubs, employer portal, direct-deposit history |
| Fixed bills with due dates | Autopay list, landlord, insurers, lenders |
| Irregular bills in the next 90 days | Car registration, tuition, annual premiums |
| Starting checking balance | Today’s Ally, Capital One, local credit-union, or bank app |
| Known extras | Travel, medical copays, gifts already promised |
If bill timing is the weak spot, fix scheduling with Bill pay without late fees while you forecast.
Three columns that matter
- Inflows: each paycheck or benefit deposit by date.
- Outflows: each bill and planned spend by date (not “average groceries” only, put the weeks that run hot).
- Running balance: start + inflows − outflows after each event.
The forecast fails when you average a month and ignore the Friday before rent. Biweekly pay quirks: Paycheck budgeting for biweekly pay.
Worked example: 90 days for Maya
Maya starts September 1 with $1,840 in checking. Net pay is $2,400 on the 7th and 21st each month (Ally direct deposit). Rent $1,550 is due the 1st. Auto loan $385 is due the 12th. Car insurance $210 hits October 3. A $600 dental bill is due November 15.
| Date | Event | Running balance |
|---|---|---|
| Sep 1 | Start; rent −$1,550 | $290 |
| Sep 7 | Pay +$2,400 | $2,690 |
| Sep 12 | Auto −$385 | $2,305 |
| Sep 21 | Pay +$2,400 | $4,705 |
| Oct 1 | Rent −$1,550 | $3,155 |
| Oct 3 | Insurance −$210 | $2,945 |
| … | (pattern continues) | … |
| Nov 15 | Dental −$600 | Depends on grocery discipline |
The scare is September 1–6, not the monthly average. Maya cannot safely “move rent autopay after September 7” while rent is still due September 1 unless the landlord agrees in writing to a new due date. Practical fixes: keep a one-month rent buffer in HYSA so Sep 1 clears before the Sep 7 paycheck, ask the landlord about a due-date change, or trim discretionary spend before the 1st. That buffer logic is the same muscle as an emergency fund, sized for timing, not only catastrophes. Annual and semi-annual bills belong in a sinking line (Save for irregular bills).
How to build yours in 30 minutes
- List every inflow date for the next 90 days.
- List every fixed outflow date; add known irregulars.
- Sort by date; compute the running balance.
- Highlight any day the balance would fall under your personal floor (many people use $300–$1,000).
- Fix troughs: ask creditors/landlord to shift due dates in writing, pause nonessential autopay, or pre-move cash from savings the day before.
- Revisit every two weeks when a paycheck or bill changes.
Forecast vs budget vs net worth
| Tool | Horizon | Question |
|---|---|---|
| Budget | This month’s categories | Am I overspending groceries? |
| Cash-flow forecast | Next 90 days by date | Will I clear on the 1st? |
| Net worth | Quarterly snapshot | Are assets minus debts rising? |
Use all three. Do not let a rising Fidelity 401(k) convince you the checking trough on the 1st is imaginary.
Checklist
- Export or write 90 days of pay dates and net amounts.
- Add every fixed due date and known irregular bill.
- Build a running balance from today’s checking figure.
- Mark troughs below your floor.
- Change timing or cash location before the trough hits.
- Refresh the sheet after any new autopay, raise, or medical bill.
Educational only. Not financial-planning or tax advice. Your due dates, bank posting times, and pay calendar control the math.