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 either moves rent autopay to the day after payday, keeps a one-month rent buffer in HYSA, or trims 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: shift due dates, 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.