How to calculate cash flow for a small service business.

Cash flow is the single most important number for a small service business. More important than revenue, more important than profit, more important than any other financial metric until the business is large enough to have a CFO. Profitable businesses still go under when cash flow gets sideways; unprofitable businesses can survive a long time if cash flow stays positive.

This guide walks the simple formula, the three places small businesses miscount, a real worked example, and the three habits that fix most cash-flow problems without hiring an accountant.

That is the whole thing. Three notes that matter:

• Cash collected, not revenue billed. If you sent $20K in invoices but only $14K cleared the bank, your cash collected is $14K. The other $6K is accounts receivable, not cash.
• Cash paid, not expenses incurred. If a supplier billed you $3K this month but you paid them last month, that $3K is not in this month's cash flow.
• In a specific period. Pick a window (weekly, monthly, quarterly) and use the same window every time. Mixing periods produces meaningless numbers.

Cash flow and profit can diverge significantly. A business can be profitable on paper while running negative cash flow because customers owe a lot and have not paid yet. The reverse is also true: a business can run positive cash flow while being unprofitable because it is being paid up front for work not yet performed.

Walk through one month for a solo HVAC operator with one assistant. Numbers are simplified for clarity.

Money in (cash collected)

• Card payments via Stripe: $24,800
• Check payments cleared this month: $4,200
• Cash payments deposited: $1,100
• Maintenance contract auto-charges: $1,800
• Total cash collected: $31,900

Money out (cash paid)

• Parts and supplies: $4,300
• Subcontractor (assistant): $5,600
• Truck (gas, insurance, payment): $1,250
• Software (FSM, QBO, payment processing): $250
• Insurance and licenses: $400
• Marketing (Local Services Ads): $1,800
• Rent on small office/storage: $800
• Phone, utilities: $200
• Owner draw (paid to personal account): $8,000
• Total cash paid: $22,600

Cash flow for the month

Note what is NOT in this calculation: the $3,500 in outstanding invoices customers have not paid yet, the $1,200 owed to a supplier who has not invoiced yet, and the depreciation on the truck. Those affect profit, not cash flow.

Mistake 1, confusing AR with cash

Outstanding invoices are not cash. A business with $15K in cash and $8K in outstanding AR has $15K to spend this month, not $23K. The AR is real and probably will turn into cash eventually, but eventually does not pay rent.

Mistake 2, treating credit-card sales as instant cash

Most card processors (Stripe, Square) settle T+1 to T+2. A card payment posted on Friday clears your bank on Monday or Tuesday. For weekly cash flow tracking, this rarely matters. For day-of-the-week cash flow (especially around payroll), it can.

Mistake 3, missing the owner draw

Money you transfer from the business account to your personal account is cash out of the business. If you do not include the draw in the cash-paid number, you overstate the business's cash flow. This shows up when owners say 'we had a great month' but the business account never grows.

Mistake 4, ignoring seasonal timing

HVAC, lawn care, snow removal, and other seasonal trades have predictable cash-flow swings. The right window for cash-flow analysis is 3-12 months, not 1 month. A single bad month is not a problem; three bad months in a row is.

Habit 1, invoice same-day

Single biggest lever. Invoices sent same-day get paid an average of 14 days faster than next-week invoices. Compress the time from work-complete to invoice-sent to under 6 hours and your cash flow improves regardless of anything else.

Habit 2, collect by card link, not check

Card payments via public link clear T+1 to T+2. Check payments clear 5-14 days after the customer decides to send them, plus mail time. Pay processing fees (2.9% + 30¢) to gain 7-14 days of cash. The math almost always works in your favor.

Habit 3, watch your AR aging weekly

Every Friday, 5 minutes. How much is outstanding, how much is past due, how much is over 30 days old? Pattern recognition. If past-30 climbs three weeks in a row, you have a follow-up problem. If over-60 grows, you have an escalation problem.

Once revenue is over ~$200K/year or the team is over 3 people, ad-hoc cash-flow tracking starts breaking down. Build a simple rolling forecast:

• Spreadsheet with 12 monthly columns, current month first.
• Expected revenue per month based on bookings, contracts, and seasonal patterns.
• Fixed expenses per month (rent, insurance, software, salaries, owner draw).
• Variable expenses based on revenue (parts, subcontractor labor, processing fees).
• Capital expenditures (new truck, equipment).
• Running cash balance at month-end.

Update monthly. The forecast does not need to be accurate; it needs to be a habit. The act of forecasting catches problems 6-8 weeks before they hit, which is enough time to do something about them.

1. Confirm it is real. Are you including all cash in and all cash out? Are you in a seasonal trough? Sometimes the negative number is a timing artifact.
2. Accelerate collections. Run the AR aging report; pick the 5 oldest invoices and follow up today. Convert any late checks to card payments with a discount if needed.
3. Defer non-essential spending. Marketing budget, new equipment, software upgrades, all postponable.
4. Negotiate with suppliers. Most are willing to accept 30-day terms instead of 15 if you ask early. Bad communication with suppliers is the fastest way to make a temporary problem permanent.
5. Talk to your bank about a line of credit. Set one up before you need it. Lines of credit are cheap when you don't need them and expensive (or unavailable) when you do.
6. Cut owner draw before cutting employee pay. Employees leaving over a missed paycheck creates a worse problem than a tough personal month.