Your P&L answers "am I profitable?" A 13-week cash flow forecast answers the question that actually closes ecommerce stores: "can I pay the supplier balance on the Thursday it's due?"
The email from your supplier is polite and non-negotiable: the balance on your fall inventory order is due when the container ships, two weeks from Friday. It's a number you agreed to months ago. You open your banking app, look at the balance, and do the mental math you've done a hundred times — payouts coming in, payroll going out, that sales tax filing sometime soon — and realize you genuinely don't know if the money will be there.
Which is strange, because the business is fine. Last quarter was profitable. Your accountant said so. But you've also lived the other version of this moment — the one where the mental math was wrong, the supplier payment bounced against a thin week, and you spent two days moving money between accounts and drafting an apologetic email to the one vendor you can't afford to annoy.
The belief that keeps putting you back in that moment is a simple one: "I'm profitable, so the cash will take care of itself." For most businesses that's merely optimistic. For a store that holds inventory, it's structurally false — because profit accrues smoothly across a quarter, and your cash leaves in lumps. A 13 week cash flow forecast is the ecommerce-specific fix: one spreadsheet, fifteen rows, updated every Monday, that shows you the bad week while it's still six weeks away.
Why 13 Weeks — and Why Weekly
Thirteen weeks isn't an arbitrary horizon. It's one quarter — which for most stores is also roughly one full inventory cycle: place the PO, pay the deposit, pay the balance at shipping, receive the goods, sell through, and collect the cash. A shorter forecast can't see a purchase order's whole life. A longer one is guesswork dressed up as planning.
The weekly granularity matters even more than the length. Monthly cash forecasts — the kind most accounting software produces by default — average away exactly the thing that kills inventory-heavy stores. A month where $95,000 comes in and $90,000 goes out looks comfortable. But if $58,000 of that outflow lands in the second week, against $21,000 of receipts, you were deeply negative for eight days in the middle of a "fine" month. Your bank doesn't average. Your supplier doesn't either.
Weekly columns are the finest resolution you can maintain in 30 minutes a week, and the coarsest resolution that still catches the crunch. That's the whole design.
The Rows That Make It an Ecommerce Forecast
A generic small-business cash forecast will fail you here, because ecommerce money has timing behaviors that generic templates don't model. Five of them do most of the damage:
Payouts arrive on payout cadence, not sales date. The sales you make this week are not this week's cash. Shopify batches them, deducts fees and refunds, and deposits on its own schedule — which is why your payout never equals your sales. Forecast the deposit, on the day it lands, net of what actually comes out of it. If you forecast sales instead of payouts, every column is wrong by a few days and a few percent — enough to hide a red week.
Inventory PO payments are the lumpy killer. Payroll and ad spend are rhythmic. A purchase order is not: a deposit at placement, a large balance at shipping, sometimes a final tranche on delivery terms. For an inventory-heavy store, a single seasonal PO can equal three or four weeks of total receipts, due on one specific Thursday. This is the row the whole forecast exists to protect you from.
Financing remittances come out weekly. If you've taken a Shopify Capital-class advance, a fixed slice of your sales leaves before the payout even reaches your bank — a remittance that's mostly principal, not expense, but it's 100% cash either way. Forecast it as its own outflow row. One caution: if the remittance is deducted inside your payout, forecast the payout gross and keep the remittance row, or forecast it net and delete the row — never both, or you'll double-count the outflow.
Sales tax leaves in specific weeks. The sales tax you collect all quarter isn't yours, and it exits in concentrated remittance weeks — monthly or quarterly depending on your filing schedule and states. A monthly filer remitting around the 20th has a predictable four-figure outflow in the same week of every month. Put those weeks in the forecast explicitly. (Filing cadences vary by state and by your volume — confirm yours with your CPA.)
Gateways and BNPL pay on their own clocks. PayPal, Klarna, Shop Pay Installments — each settles on its own cadence, some within days, some holding reserves. If a meaningful share of your checkout runs through them, they need their own receipts row with their own timing, not a blend into the Shopify number.
The Build: 15 Rows, 13 Columns
Open a blank spreadsheet. Thirteen columns, one per week, starting Monday. Fifteen rows:
| # | Row | Where the number comes from |
|---|---|---|
| 1 | Shopify payouts | Payout schedule × recent weekly average, adjusted for seasonality |
| 2 | Other gateway / BNPL payouts | Each provider's settlement cadence |
| 3 | Wholesale / B2B collections | Open invoices, by due date (then by realistic pay date) |
| 4 | Other cash in | Marketplace payouts, rebates, anything else |
| 5 | Inventory PO payments | Deposits and balances from PO terms, by due date |
| 6 | Freight, duties & customs | Shipment schedule; brokers invoice near arrival |
| 7 | Payroll & contractors | Your pay calendar |
| 8 | Ad spend | Card settlement dates, not campaign dates |
| 9 | Software & fixed opex | Subscription billing dates |
| 10 | Rent / 3PL invoices | Lease and 3PL billing cycle |
| 11 | Sales tax remittances | Your filing calendar |
| 12 | Financing remittances | Advance terms (see the double-count warning above) |
| 13 | Net cash flow | Rows 1–4 minus rows 5–12 |
| 14 | Beginning cash | Prior week's ending cash |
| 15 | Ending cash | Row 14 + row 13 — the only number that matters |
Now walk it with fictional round numbers. Say your store does about $105,000 a month: Shopify payouts run $22,000 a week (softening to $19,000 in a seasonal dip around weeks 5–7), plus $2,500 a week from other gateways. You start with $14,000 in the bank. You've just placed an $84,000 fall inventory PO — 30% deposit in week 2, the balance-at-shipping portion of $33,600 due week 6, freight and duties of $4,500 arriving week 7. Payroll runs $3,600 weekly, ads $6,000, opex $1,400, a Capital-class remittance about $3,000, 3PL invoices $3,800 monthly, and sales tax around $8,400 remitted in weeks 3, 7, and 12.
Here's what rows 13 and 15 do across the first nine weeks (thousands):
| Week | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|
| Net cash flow | +6.7 | −14.7 | +2.1 | +10.5 | +3.7 | −26.1 | −5.1 | +10.5 | +14.7 |
| Ending cash | 20.7 | 6.0 | 8.1 | 18.6 | 22.3 | −3.8 | −8.9 | 1.6 | 16.3 |
There it is. Weeks 6 and 7 are red. Not because the business is failing — week 9 is comfortably positive again — but because the PO balance, the freight bill, and a sales tax remittance all land inside the seasonal payout dip. No monthly view catches this: the quarter nets positive, and even each individual month roughly washes out. Only the weekly cumulative row shows you the eight days where the bank balance goes below zero.
Every number above is illustrative and deliberately round. The point isn't the figures — it's that your store has its own version of week 6, and right now it's invisible.
The Monday Update: 30 Minutes From Reconciled Books
A forecast you built once is a souvenir. The tool is the cadence: every Monday morning, 30 minutes.
The routine is mechanical. Replace last week's forecast column with actuals. Note where you were wrong — payouts lighter than expected, an invoice that slipped — and adjust the remaining weeks with what you learned. Add a new week 13 at the far end. Check the ending-cash row for anything red or close to it. Done.
Here's the part that decides whether those 30 minutes are real: your forecast is only as good as the books it starts from. "Replace forecast with actuals" assumes you have actuals — payouts reconciled to the bank, fees separated from revenue, refunds where they belong. If your books run weeks behind, every Monday starts with an archaeology session and the forecast quietly dies by week four. Clean, current books are the foundation the whole exercise stands on — it's the same infrastructure your taxes and your margins depend on. This is where a sync tool earns its keep in a way that has nothing to do with bookkeeping for its own sake: LedgerPort keeps Shopify and WooCommerce payouts reconciled in QuickBooks automatically, which means Monday's "actuals" are already sitting there when you open the forecast.
And if an accounting firm runs your books, ask them for this — a rolling 13-week forecast is a deliverable good ecommerce firms already produce from the reconciled file they maintain anyway.
What You Actually Do About a Red Week
The forecast doesn't fix week 6. It buys you six weeks to fix it — and almost everything on the menu works at six weeks out and fails at six days out:
- Move the PO, not the payroll. Ask the supplier to split the shipment — half the balance at shipping, half on delivery — or shift the ship date two weeks. Suppliers handle this routinely when asked early; they handle it badly when your payment is already late.
- Negotiate terms while you don't need them. A 30/40/30 payment structure instead of 30/70, or net-30 on the balance, moves tens of thousands across week boundaries. Terms are easiest to win when your books are clean and your ask is specific: "our cash model shows the crunch — can we split the balance?"
- Pull collections forward. If you sell wholesale, week 6 is why your B2B invoices need due dates, reminders, and proper AR tracking in QuickBooks. A $8,000 invoice collected in week 5 instead of week 9 can erase half the problem.
- Arrange financing calmly instead of desperately. If the gap is real and the fixes above don't close it, a line of credit negotiated in week 1 is cheap insurance; the same money found in week 6 is expensive and rushed. Just remember the remittances become a new row 12.
Notice what all four have in common: they're phone calls, not crises. That's the entire return on the spreadsheet. The store that sees week 6 in week 1 makes a routine ask of a supplier. The store that discovers week 6 in week 6 makes an apology.
The Thursday, Revisited
Go back to that supplier email. Balance due in two weeks, and you didn't know if the money would be there. With this spreadsheet, that becomes a question you answer in ten seconds — scroll to the column, read row 15. Either it's fine and you stop thinking about it, or it's red and you have two weeks and four options instead of a bad Thursday.
Fifteen rows. Thirteen weeks. Thirty minutes on Mondays — provided the books feeding it are already reconciled, which is the one input worth automating. If your payout reconciliation still runs on export-and-cleanup, that's the first fix; LedgerPort's free plan is a low-stakes way to get the actuals flowing while you build the forecast around them.
