Every PE-backed portfolio company has a 13-week cash flow. Almost none of them use it well. Most build the model once, run it monthly, and stop reconciling actuals against forecast after week 4 because the variance embarrasses them. That is not a 13-week cash flow. That is a static forecast that dies in a filing cabinet. This is how to build one that actually runs your cash operations.

This is the operational version. If you want the AI-assisted build with prompts and templates, see Rolling 13-Week Cash Flow With Claude. This piece is about the model that runs your Monday meeting.

Why the 13-week horizon

Thirteen weeks is one quarter. It is short enough that AR and AP timing dominate (weekly precision matters) and long enough that payroll cycles, monthly debt service, and quarterly tax payments all land inside the window. Anything shorter and you cannot see the debt covenant. Anything longer and you are running a P&L forecast, not a cash forecast.

AFP’s 2025 Treasury Benchmarking Survey reported that 78 percent of PE-backed portfolio companies now run a formal 13-week model, up from 51 percent in 2019. The lift traces to two things: lender covenants tightening, and sponsor operating partners adopting the model as the standard weekly artifact.

Data to pull, and where it lives

How to model AR collections

AR collections is the single hardest line. It is also 60 to 70 percent of inflows for most businesses, so it is worth getting right.

Do not use “AR aging bucket rolled forward by DSO.” That is what most models do and it is why they miss so badly. Build it by customer for the top 20 customers, and by bucket for the rest.

For the top 20:

• Pull the open AR by invoice
• Attach the customer’s actual payment history (median days past due, not average, avoid outlier distortion)
• Project each invoice into the week it will actually collect

For the long tail:

• Use aging bucket, use a historical collection curve (percent collected in weeks 1, 2, 3, 4, 5+)
• Apply the curve to the current bucket balance

This mixed approach usually explains 90 percent of collections in the right week. Pure bucket rolls explain about 65 percent. That gap is why the variance conversation matters.

How to handle payroll, AP, and debt

Payroll: Semi-monthly or biweekly, so payroll lands in specific weeks. Do not smooth. Show the spike. HR owns the number because HR knows the new hires and the exits.

AP: Split into two buckets. Approved payment run for the week (deterministic) and open AP by vendor with a payment-terms projection (probabilistic). Most models miss the probabilistic bucket. Vendors with 30-day terms do not all get paid on day 30. Some get paid at 25. Some at 40. Track the actual pattern per vendor category.

Debt service: This is the easy line. Take the amortization schedule out of the credit agreement, lock it into the model, do not touch it. Interest on revolver moves with balance, so tie it to a formula. Every other debt line is deterministic.

The weekly ritual: what happens every Monday

1. 7:30am. Controller pulls opening cash from bank feeds. Reconciles against last week’s closing forecast. Delta gets logged.
2. 8:00am. Collections lead updates prior-week actual collections. By customer for top 20, by bucket for the rest.
3. 8:30am. AP lead updates prior-week disbursements. Approved payment run for the coming week is drafted.
4. 9:00am. FP&A refreshes the model. Rolls forward one week (drops the historical week that just closed, adds a new week 13 on the far end).
5. 10:00am. Cash meeting. CFO, Controller, Collections, AP, and CEO if the number moves. Focus on variance vs last week’s forecast, decisions on this week’s payment run, and any customer at risk.
6. By EOD Monday. Updated 13-week distributed to sponsor operating partner if the operating cash trend materially changed.

Under two hours, every Monday. If the ritual takes longer, the model is too complicated or ownership is unclear.

Why the reconciliation matters more than the forecast

The forecast is the artifact. The reconciliation is the tool. Every week you produce forecast vs actual variance by line. Where you were wrong tells you what assumption to adjust.

Example: forecast said $2.4M of collections week 3. Actual was $1.9M. $500K miss. Split by top customer: Customer A paid on time. Customer B paid $600K instead of $800K. Customer C did not pay at all (was assumed at $200K). Now you know the story. Customer C goes on the CFO call list. Customer B goes on the aged-invoice list. Adjust the next forecast accordingly.

Do this for 8 weeks and the model gets meaningfully sharper. Do this for 26 weeks and the model becomes a management tool the sponsor uses to underwrite decisions.

What variance actually tells management

Variance is a diagnostic, not a scorecard. Three questions to ask every week:

• Was the miss timing or structural? Timing corrects the next week. Structural does not.
• Was the miss customer-specific or across the base? Specific = collections issue. Across the base = a payment terms trend.
• Is the miss going to compound? A single customer 5 days late is noise. Every enterprise customer 5 days late is a change in behavior and needs a policy response.

The 5 assumptions that break every forecast

1. DSO by customer. Not blended DSO. Median DSO per top customer. If you build against blended, you will miss the shape of the weeks.
2. AP payment timing. Vendors do not all get paid on day 30. Track by vendor category.
3. Payroll timing. Semi-monthly does not equal biweekly does not equal weekly. Get the calendar right.
4. Sales-driven inflows. Do not model closed deals as cash the week they close. Model them as cash the week the invoice payment terms mature.
5. Non-recurring items. Tax refunds, insurance rebates, one-time credits. If you slot them wrong, the model looks great on paper and fails in practice.

Sponsor and lender visibility

The 13-week cash flow is not just an internal artifact. Sponsor operating partners want it monthly, at minimum. Some sponsors want it weekly. Lenders under a credit agreement usually want it monthly and reserve the right to ask for weekly if the borrowing base tightens.

Distribute the same version to everyone. Do not maintain a “clean” version for lenders and a “real” version for internal use. Sponsors and lenders talk. The version you send is the version you use.

Where this connects

The 13-week reconciles into the monthly close (opening cash on WD1). See the monthly finance cadence for how the two artifacts sit together. It also lives inside the MBR pack, which is covered in the PE-backed CFO board reporting package. And in the first 90 days at a portfolio company, building this model is a top-3 priority. See the first 90 days as a portfolio company CFO.

FAQ

Do I need a treasury workstation, or is Excel fine?
Excel is fine for anything under about $500M revenue. The value is the discipline, not the software. If you outgrow Excel, the trigger is usually multi-entity consolidation or bank complexity, not the model itself.

How many weeks of history should I keep in the model?
Keep the last 4 weeks visible for context. Archive the rest in a history tab. Do not delete. The archived weeks are what you use to sharpen assumptions.

How do I get AP to actually update on time?
Tie it to the Monday cash meeting. If AP does not show up with prior-week actuals and this-week’s payment run, the meeting cannot happen. Force the discipline.

What if we have a revolver?
Model the revolver as a plug against a target minimum cash balance. The 13-week then shows required borrowings by week. That is the number the lender actually cares about.

Can AI build this?
AI can draft the structure, build the formulas, and speed up the Monday reconciliation. Assumptions and ownership stay with the humans. See the AI-assisted version for the prompt library.

Sources

• AFP (Association for Financial Professionals), “Treasury Benchmarking Survey,” 2025
• AlixPartners, “Liquidity Management in PE-Backed Companies,” 2025
• Grant Thornton, “Middle Market Report: Cash and Working Capital,” 2025
• Bain & Company, “Global Private Equity Report,” 2026

Written by The Pragmatic CFO. 15+ years running FP&A and finance operations across PE-backed portfolio companies.