Why thirteen weeks
Thirteen weeks is one quarter. It is long enough to see problems coming and short enough that your guesses are reasonably good. Each week you drop the week that passed, add a new one at the end, and compare what happened to what you expected.
Because it is a rolling view, it keeps you honest about customer payment timing and big bills.
Build the layout
Use a spreadsheet with weeks across the top. Rows start with the opening bank balance, then cash coming in, cash going out, and the closing balance. The closing balance of one week is the opening of the next.
Under cash in, list customer collections, deposits, loan proceeds and owner contributions. Under cash out, list payroll, taxes, rent, supplier payments, loan payments, owner draws and planned purchases.
Estimate collections realistically
Use the aging report. For each large open invoice, put the amount in the week you think it will really be paid, based on how that customer pays, not on the due date. For sales not yet invoiced, estimate using normal collection time.
Be cautious here. Optimistic collections are the main reason forecasts fail. If a customer is usually two weeks late, plan for it.
List payments by due date
Use the unpaid bills list and the calendar. Payroll and payroll taxes, sales tax, insurance renewals, quarterly estimated tax payments and loan payments often land on fixed dates. Put each in the right week. Include a small cushion for surprises.
Remember money that leaves monthly or quarterly rather than weekly. A forecast that only shows weekly bills will look fine until a large quarterly item arrives.
Use it to decide
Watch the lowest closing balance. If it dips below a minimum you set, act early: ask customers to pay sooner, delay a purchase, negotiate with a supplier or arrange credit. Doing it weeks ahead costs less than doing it in a crisis.
Update every week with actuals. Over a few weeks, you will learn where your estimates are weakest and improve them. Software reports help, but the forecast itself is a thinking tool, so keep it simple.
A tip on scenarios
Run two versions: the expected case and a cautious case where your three largest customers pay two weeks late. Comparing the lowest balances in each shows how exposed you are to a single late payment. If the cautious case dips below your minimum, you know exactly how much credit or reserve cash would solve the problem, and you can arrange it while banks and suppliers are still willing to listen.
Do not worry if the first version is rough. The value comes from the weekly update, when you compare what you expected with what happened and ask why. After a month, you will notice which customers pay on time, which bills you forgot, and how much cushion the business really needs.
Common questions
Is this the same as a budget?
No. A budget plans profit by month. A cash forecast tracks the timing of money by week.
Do I need accounting software for it?
Software provides the inputs such as aging and bills, but a spreadsheet is usually used for the forecast.
How long does it take to maintain?
Once built, many owners need less than an hour a week.
This guide is general information, not tax, legal or accounting advice. Rules, fees and due dates change; check with the IRS, the NJ Division of Taxation or a licensed professional for your situation.