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13-Week Cash Flow Calculator for Small Business

Model weekly collections and disbursements, see the lowest projected cash point, and test what happens when receipts slow or expenses increase.

No account required Educational, not individualized advice

Forecast assumptions

Use expected cash timing, not accounting revenue. All recurring values are weekly.

Cash grows in this scenario

Ending cash

$166,000

Lowest week

$107,000

13-week change

$66,000

Projected weekly cash

1
2
3
4
5
6
7
8
9
10
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12
13
WeekReceiptsDisbursementsEnding cash
1$50,000$43,000$107,000
2$50,000$43,000$114,000
3$50,000$43,000$121,000
4$50,000$43,000$128,000
5$50,000$43,000$135,000
6$50,000$68,000$117,000
7$50,000$43,000$124,000
8$50,000$43,000$131,000
9$50,000$43,000$138,000
10$50,000$43,000$145,000
11$50,000$43,000$152,000
12$50,000$43,000$159,000
13$50,000$43,000$166,000

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Worked example

A service business with $50,000 of weekly collections and a $25,000 payment in week 6

A service business starts the quarter with $100,000 in the bank. It expects $50,000 of customer collections a week against $22,000 of payroll, $18,000 of other operating cash, and $3,000 of debt payments. A $25,000 one-time payment, such as an equipment deposit, falls in week 6. These are the prefilled inputs in the calculator.

Inputs

Worked example inputs
Opening cash$100,000
Weekly customer collections$50,000
Weekly payroll and benefits$22,000
Other weekly operating cash$18,000
Weekly debt payments$3,000
One-time outflow$25,000 in week 6
Collections scenario0%

Calculator output

Worked example calculator output
Week 6 ending cash$117,000
Lowest week$107,000 (week 1)
Ending cash, week 13$166,000
13-week change$66,000

Each normal week nets $7,000 ($50,000 in, $43,000 out), so 13 weeks add $91,000 before the $25,000 payment. Move the collections slider to 20% lower and the same inputs show $36,000 of ending cash, with the low point in week 13: the business burns $3,000 a week and the forecast shows it before the bank balance does.

Methodology

How this calculator works

The calculator rolls cash forward one week at a time for 13 weeks using the receipts and disbursements you enter. It reports ending cash, the lowest weekly balance, and the change over the period.

Formulas

  • Weekly receipts = weekly collections x (1 + collections scenario %) + any one-time inflow in the event week.
  • Weekly disbursements = payroll + other operating cash + debt payments + any one-time outflow in the event week.
  • Ending cash for a week = prior week ending cash + receipts minus disbursements, starting from opening cash.
  • Lowest week = the smallest weekly ending balance; 13-week change = week 13 ending cash minus opening cash.

Assumptions

  • Every recurring amount is the same each week; the collections scenario scales collections only.
  • One-time inflow and outflow both land in the single event week you choose.
  • Amounts are cash timing, not accrual revenue or expense.

What it ignores

  • Tax payments such as quarterly estimates and payroll deposits unless you include them in the weekly amounts.
  • Seasonality, irregular payroll weeks, credit line draws, and interest on cash.
  • Accounts receivable aging and vendor payment terms beyond what your weekly estimates reflect.

Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last reviewed October 20, 2026. Taxstra is a CPA firm for high income earners, business owners and real estate investors, serving 1,000+ clients in all 50 states.

Educational, not individualized tax advice.

Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last updated October 20, 2026.

How to use the result

The forecast is a management conversation, not a prediction contest

Use the model to expose timing, assumptions, and decisions. Update actual cash and collections every week; do not leave the original forecast untouched for a quarter.

01

Start with timing

Revenue on the income statement is not the same as cash collected. Enter expected receipts based on invoice and payment behavior, not the month work is performed.

02

Separate committed and optional cash

Payroll, debt, taxes, and signed vendor commitments behave differently from discretionary hiring, equipment, owner payments, and growth spending.

03

Watch the low point

Ending cash matters, but the lowest weekly point determines whether payroll, debt, or investment decisions create a short-term liquidity problem.

Base, downside, and action scenarios

A useful forecast shows what management can change before the low point arrives.

Swipe horizontally to compare

ScenarioCollections assumptionExpense assumptionManagement use
BaseMost likely payment timingCurrent operating planNormal weekly cash management
DownsideReceipts arrive later or below planCommitted costs continueDefine trigger points and protective actions
GrowthSigned work and realistic pipelineHiring and delivery capacity addedTest whether growth can fund itself
ActionBase receiptsSpecific change such as delayed hire or faster collectionsCompare a decision before approval

Take the next planning step

Take the 13-week model into your operating meeting

Get the editable weekly forecast structure, assumption notes, scenario prompts, and a cash-review meeting agenda.

Get the editable forecast pack

Includes the weekly model, assumption notes, scenario prompts, and meeting agenda.

Frequently asked questions

What is a 13-week cash flow forecast?

It is a weekly projection of cash receipts and disbursements over roughly one quarter. The short interval helps management see collection timing, payroll, debt, taxes, vendor payments, and upcoming decisions before they affect the bank balance.

Should I use revenue or collections?

Use expected cash receipts. Start from invoices, contracts, payment terms, and actual customer behavior. Revenue may be useful as a cross-check, but the forecast must reflect when money is expected to reach the account.

How often should the forecast be updated?

Update opening cash and near-term receipts and payments at least weekly when liquidity matters. Compare actual results with the prior forecast so assumptions improve instead of simply replacing the old numbers.

What expenses belong in the forecast?

Include payroll, benefits, contractors, rent, software, vendors, debt, taxes, owner payments, equipment, and other known cash events. Separate committed items from discretionary choices so management can see what can be changed.

Why is this different from a profit-and-loss statement?

The P&L measures financial performance under the accounting method. The cash forecast models timing. Receivables, payables, debt principal, asset purchases, and owner activity can move cash differently from reported profit.

When should a business get CFO help with cash flow?

Consider help when collections, payroll, debt, entities, locations, or growth decisions create material timing risk; when the forecast is not updated; or when management cannot explain why cash differs from profit.

Related services and resources

Cash-flow forecast template

Build the detailed weekly operating model.

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Outsourced CFO services

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Controller vs. CFO

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