Why it helps
Your accounting software tells you what already happened. A cashflow forecast tells you what's coming: the week the rent, wages and a GST payment all land at once, or the quiet month after Christmas. Thirteen weeks is about three months, which is long enough to see trouble coming and short enough to guess sensibly.
Setting one up from scratch is the hard part. AI can design the layout and write every formula for you, using your own rough numbers. You end up with a simple table you understand and can update each week in ten minutes.
The prompt
Copy it, swap the bits in [square brackets], and paste it into ChatGPT, Claude, Gemini or Copilot.
I run a small [type of business] in New Zealand. Help me build a simple 13-week cashflow forecast in [Excel / Google Sheets]. Use NZ English. Please: 1. Design the layout: weeks across the top (columns), money coming in and money going out down the side (rows). 2. Include rows for opening bank balance, each type of money in, total in, each type of money out, total out, net cash for the week, and closing balance. 3. Make each week's opening balance equal the previous week's closing balance. 4. Give me the exact formulas for column B (week 1) and column C (week 2), and tell me how to copy them across to week 13. 5. Fill in weeks 1 to 3 with my numbers below so I can check it works. Rules: - Only use the numbers I give you. Don't invent any income, costs, tax amounts or due dates. Where I haven't given a figure, leave the cell blank and tell me. - Keep it simple. No macros. My numbers: [starting bank balance, typical weekly sales, regular costs and how often they're paid, any one-off payments and which week]
Then keep chatting
Add conditional formatting so any week with a closing balance below $[amount] turns red.
Add a row for GST and tell me where I should get my real GST figure from.
Show me a "what if" version where sales drop 20% for weeks 5 to 8.
Explain each formula in plain English so I can fix it myself if it breaks.
Step by step
- Jot down your numbers: what's in the bank today, roughly what comes in each week, and your regular costs (wages, rent, suppliers, loan, subscriptions) with how often each is paid.
- Add any big one-offs you know about, like insurance, a GST or tax payment, or a new piece of gear. Use your real figures from myIR or your accountant, not a guess from AI.
- Paste the prompt with your numbers. Build the table in your spreadsheet using the layout and formulas it gives you.
- Check weeks 1 to 3 by hand with a calculator. If the closing balances match, copy the formulas across.
- Each week, replace last week's forecast with what actually happened, and add a new week at the end.
Worked example
Example details are made up. Your results will vary, so always read and check before you use them.
Watch out for
- A forecast is only as good as the numbers you put in. Treat the AI's numbers as layout examples, use your own, and check the first few weeks by hand. A formula pointing at the wrong cell can quietly throw everything off.
- Don't let AI guess your GST or income tax amounts or due dates. Get them from myIR, ird.govt.nz or your accountant.
- Privacy: you don't need to paste bank account numbers, staff names or customer details. Round totals are enough.
- This is a planning tool, not financial advice. If the forecast shows a real shortfall, talk to your accountant or bank early.
Go further
Once it's set up, make it a Monday habit: ten minutes, update last week's actuals, look at the next four weeks. If a few products or dishes are doing the heavy lifting, the [menu costing](/use-cases/menu-costing) use case can help you check their margins, and the [spreadsheet formula helper](/use-cases/spreadsheet-formula-helper) can fix any formula that breaks.
