How to build a 13-week cash flow forecast for a service business

What a 13-week forecast tells you

A profitable project can still leave an agency short of cash if payroll falls before the client pays. A 13-week forecast makes that timing visible. Thirteen weekly periods cover 91 days, roughly a quarter. This is a rolling cash view, not the same thing as a calendar-quarter profit and loss statement.

Use the direct method: list expected cash receipts and cash payments, then calculate the closing balance each week. Wall Street Prep's 13-week model guide describes this structure and weekly updates. Its examples focus on restructuring; the same basic arithmetic helps a healthy agency plan payment timing and spot a shortfall early.

For collections decisions, pair it with an accounts receivable aging report. Aging shows what is owed and how late it is. A forecast makes a separate judgment about when cash might arrive. Neither an invoice's due date nor a signed pipeline opportunity is a bank receipt.

Start with cash you can actually use

1. Set the cutoff and scope. Choose the first week's start date, the bank accounts and the reporting currency. Use one consistent week boundary, such as Monday through Sunday.
2. Reconcile opening cash. Compare the bank position with the ledger and explain uncleared items. Separate restricted or ring-fenced cash. If a payment has already reduced opening cash, do not include it as a future payment too.
3. Refresh open invoices. Apply known payments and credits. Record remaining balances, due dates, expected receipt dates and the evidence for each expectation.
4. Add future billing separately. Retainers, milestone invoices and new work may produce cash within 13 weeks. Include the billing trigger and payment lag, not just the month in which revenue is expected.
5. Schedule cash outflows. Use payroll dates, tax deadlines, supplier terms, rent, subscriptions, debt service and planned purchases. Include cash taxes or refunds where applicable; non-cash depreciation is not a payment.

An undrawn credit facility is not opening cash. If funding is relevant, model a draw as a separate financing receipt only when its availability, limits, conditions and timing support that assumption. Show repayments and interest separately. Transfers between your included bank accounts cancel out; they are not customer receipts or operating payments.

Build the receipt schedule from invoices

For a small service firm, start with invoice-level timing for material balances. Use a payment promise, confirmed payment run or demonstrated client pattern when available. Label unsupported dates as assumptions. Keep the contractual due date unchanged when you move a forecast receipt; a forecast revision does not amend payment terms.

The remaining $114,000 of receipts in the worked forecast comes from assumed future billing, for $159,000 total receipts. Keep those future invoices on a separate schedule until issued. When an invoice is created, move its forecast line into the open-invoice schedule using a stable reference; do not add a second receipt.

If a client plans to pay in instalments, use one row per expected receipt and reconcile the sum to the remaining balance. A $10,000 invoice with a $4,000 receipt already applied has only $6,000 left to forecast. An approved credit reduces the collectible balance; it is not cash coming into the bank.

Keep disputed amounts and unconfirmed pipeline identifiable. For example, place a disputed receipt outside the base case until there is a credible resolution path, and show an alternative scenario if helpful. Multiplying a large uncertain invoice by a probability can create a smooth-looking receipt that the client will never actually pay in that amount.

A complete 13-week cash flow example

This fictional agency starts with $40,000 of available cash. Weeks run Monday through Sunday from 21 September to 20 December 2026. All figures are illustrative USD cash amounts, not HUNT customer data. There are no financing flows or inter-account transfers in this example. Outflows combine payroll, suppliers, overhead and other scheduled cash payments; a working model should retain those categories underneath the total.

The reconciliation is $40,000 opening cash + $159,000 receipts − $182,000 payments = $17,000 closing cash. Do not sum the weekly opening or closing balances: those are snapshots. The lowest weekly closing balance is $15,000 in week 12, even though the final week closes at $17,000.

Suppose management sets a $15,000 minimum operating buffer for this example. The base case touches that buffer in week 12 and has only $2,000 headroom at the end. This buffer is an illustrative policy choice, not a recommended amount for every agency. Choose yours from payroll, commitments, cash volatility and access to funding.

Copy this spreadsheet structure

Use columns B through N for the 13 weeks. Put the week-start dates in row 1 and enter positive numbers for receipts and payments. The formulas below work with a simple single-currency model. Add separate receipt and payment schedules behind the totals so every number has an owner and a source.

Column A labels
A1: Week starting
A2: Opening cash
A3: Cash receipts
A4: Cash payments (positive amounts)
A5: Closing cash
A6: Minimum cash buffer
A7: Headroom / (shortfall)

Week 1 in column B
B1: Enter first Monday's date
B2: Enter reconciled opening cash
B3: Total expected receipts for week 1
B4: Total scheduled payments for week 1
B5: =B2+B3-B4
B6: Enter your chosen buffer
B7: =B5-B6

Week 2 in column C
C1: =B1+7
C2: =B5
C3: Total expected receipts for week 2
C4: Total scheduled payments for week 2
C5: =C2+C3-C4
C6: Enter your buffer for week 2
C7: =C5-C6

Continue the same pattern through column N.
Lowest weekly closing balance: =MIN(B5:N5)
Total 13-week receipts: =SUM(B3:N3)
Total 13-week payments: =SUM(B4:N4)
Control check (must be zero): =B2+SUM(B3:N3)-SUM(B4:N4)-N5

For each receipt schedule row, keep the invoice or forecast reference, client, amount, currency, due date, expected bank date, reason for that date, status, owner and last review date. For payments, record the supplier or category, amount, planned bank date and whether the commitment is fixed or discretionary. Do not assume every supplier payment can be moved without agreement.

Test a three-week delay before it happens

Move the $15,000 INV-D receipt from week 3 to week 6, keeping every other assumption unchanged. Remove it from week 3 and add it once to week 6. This isolates a timing risk; it does not assume the invoice is written off.

The end-of-horizon cash is still $17,000, but the delayed case breaches the chosen buffer in week 4. That is the value of weekly timing: a period total hides the point at which the firm needs to act. If the receipt slips beyond week 13 instead, final cash would be $2,000 with all other assumptions unchanged.

• Ask the account owner to resolve INV-D's acceptance blocker and obtain a credible receipt date. Use the overdue-invoice workflow if payment is already late.
• Review genuinely discretionary spending before week 4. Do not silently postpone payroll, taxes or contractual obligations in the model to make the balance positive.
• If a payment change or funding action is needed, assign the authorized decision-maker and a deadline before the shortfall. Record an agreement before treating revised terms as confirmed.
• Keep the base case and delay case visible together so the team can tell which outcome relies on the client paying promptly.

Roll forward with actual receipts, not old promises

1. Save the prior forecast before editing it. Preserve the assumptions that were known at the time.
2. Replace the completed week with actual bank receipts and payments, then reconcile its closing cash.
3. Compare actuals with the saved forecast by receipt and payment category. Mark timing changes separately from amount changes or omitted items.
4. Remove settled invoices, update remaining balances and revisit missed promises. Do not carry an overdue receipt into next week indefinitely without a new reason.
5. Use reconciled closing cash as the next opening balance, add a new week at the far end and refresh scenarios and decision owners.

For example, if week 1 receipts are $10,000 against $12,000 forecast, the receipt variance is −$2,000. If payments are $10,000 against $9,000 forecast, payments are $1,000 higher. Actual closing cash is $40,000 + $10,000 − $10,000 = $40,000, or $3,000 below the original $43,000 forecast. Explain both movements instead of changing opening cash to hide the difference.

Week reviewed:
Forecast version compared with actuals:
Reconciled closing cash:
Receipt variances: timing / amount / omitted item
Payment variances: timing / amount / omitted item
Unmatched bank items and owner:
Missed receipt assumptions and revised evidence:
Lowest projected cash week:
Headroom against the agreed buffer:
Scenario requiring action:
Decision, authorized owner and action deadline:
New week added through:

Make this part of the weekly agency AR review. The collections team supplies payment evidence and unresolved blockers; finance owns cash reconciliation and the model; the founder or finance lead decides how to respond to exposure.

Common forecasting questions

Can I use DSO to forecast receipts?

Days sales outstanding can support a broad timing assumption for a stable, diversified book of invoices. It is less useful for scheduling a large milestone payment or a disputed balance. Use invoice-level evidence for material receipts and document where a general lag assumption fills a gap.

Where do advance retainers belong?

Cash already received belongs in opening cash if it is within your chosen available-cash scope; do not forecast it again when the service month begins. Future retainer cash goes in its expected receipt week. Whether an advance is earned revenue is a separate accounting question. Agree the timeline using clear agency retainer payment terms.

Does the forecast guarantee that cash will be available?

No. It is an estimate built from records and assumptions. Its usefulness comes from making those assumptions explicit, testing delays and comparing them with actual cash every week. HUNT's developing product can be explored through early access, but live AI outreach and reply delivery are still in development; the example here does not demonstrate automated collection results.