The SaaS business model: how subscription software makes money
How recurring revenue, gross margin, acquisition cost and churn fit together, worked through with one 100-customer example month by month.
Investors and advisors keep talking about retention, payback and net revenue, and all you can see is a column of monthly invoices. The gap is real: a SaaS business is judged on numbers that do not appear on any single invoice, because the model makes money slowly, from the same customers, month after month. This guide builds those numbers from scratch with one small example you can redo in a spreadsheet.
If “SaaS” itself needs a definition first, read What is SaaS?. The pricing choices that set the monthly number are compared in SaaS pricing models.
Recurring revenue in plain terms
Think of a bucket with a tap above it and a small hole in the bottom. The tap is new customers. The hole is churn, the customers who cancel. The water level is your monthly recurring revenue (MRR): the sum of what every active customer pays per month. Every month the tap adds some water and the hole lets some out. The business grows only when the tap runs faster than the hole leaks, and the hole gets bigger as the bucket fills, because churn is a percentage of what you have.
That is the whole model. Four numbers describe it:
- MRR (monthly recurring revenue): active customers times the average price per month. Multiply by 12 for ARR (annual recurring revenue). Neither is “revenue” in the accounting sense; a signed annual contract is a booking until each month of service is delivered.
- Churn: customers lost in a period as a share of customers at the start. Say which kind: logo churn counts customers, revenue churn counts dollars. This guide uses monthly logo churn.
- CAC (customer acquisition cost): sales and marketing spend divided by new customers won in the same period.
- Gross margin: revenue minus the cost of delivering the service (hosting, support, third-party fees), as a share of revenue. Software is cheap to deliver once built, so SaaS gross margins are high. Salesforce reported gross profit of $32,255 million on revenues of $41,525 million for fiscal 2026 (ended January 31, 2026), per its annual report on Form 10-K. That works out to a gross margin of 77.7%. The same filing says subscription and support made up approximately 95% of total revenues.
Why do investors care about retention more than about this month’s sales? Because a customer who stays pays every month without a new sales cost. Growth bought with the tap is expensive; growth kept by plugging the hole is nearly free.
Twelve months of one small SaaS company
Example: a company starts the year with 100 customers paying $50 a month each. Every month it loses 3% of the customers it started the month with (rounded to whole customers) and wins 10 new ones. Each new customer costs $600 to acquire, so acquisition spend is 10 x $600 = $6,000 a month. Gross margin is 80%, so each dollar of MRR leaves $0.80 after hosting and support. Round numbers, fictional company.
The arithmetic for month 1: churned customers = 3% of 100 = 3; customers at month end = 100 - 3 + 10 = 107; MRR = 107 x $50 = $5,350; gross profit = 80% of $5,350 = $4,280; minus $6,000 of acquisition spend leaves -$1,720. Repeat for 12 months.
| Month | Customers at end | MRR | Gross profit (80%) | Cumulative gross profit minus acquisition spend |
|---|---|---|---|---|
| 1 | 107 | $5,350 | $4,280 | -$1,720 |
| 2 | 114 | $5,700 | $4,560 | -$3,160 |
| 3 | 121 | $6,050 | $4,840 | -$4,320 |
| 4 | 127 | $6,350 | $5,080 | -$5,240 |
| 5 | 133 | $6,650 | $5,320 | -$5,920 |
| 6 | 139 | $6,950 | $5,560 | -$6,360 |
| 7 | 145 | $7,250 | $5,800 | -$6,560 |
| 8 | 151 | $7,550 | $6,040 | -$6,520 |
| 9 | 156 | $7,800 | $6,240 | -$6,280 |
| 10 | 161 | $8,050 | $6,440 | -$5,840 |
| 11 | 166 | $8,300 | $6,640 | -$5,200 |
| 12 | 171 | $8,550 | $6,840 | -$4,360 |
Four things the table shows that the invoices never would:
- MRR grew 60% and the company still lost money for the year. Cumulative gross profit was $67,640; acquisition spend was $72,000. Growth is paid for up front and recovered later. This is normal, and it is why SaaS companies raise money.
- The turning point is month 8, when monthly gross profit ($6,040) first exceeds monthly acquisition spend ($6,000). From there the hole in the cumulative line starts closing.
- Churn is eating more every month. Three customers left in month 1 and five left in month 12, at the same 3% rate, because the base is bigger. Churned MRR went from $150 to $250 a month. New customers must first replace those before adding anything.
- CAC payback is 15 months. Each customer contributes $50 x 80% = $40 of gross profit a month, so a $600 CAC is repaid after $600 / $40 = 15 months. A customer who churns in month 10 never paid back what it cost.
Two more numbers fall out of the same inputs. At 3% monthly churn the average customer stays about 1 / 0.03 = 33 months, so lifetime gross profit per customer (LTV, customer lifetime value) is 33 x $40 = about $1,333, and LTV divided by CAC is 2.2. Cut churn to 2% and the lifetime becomes 50 months, LTV $2,000 and the ratio 3.3, with no change to price or sales spend. That single lever is why “retention” is the word you keep hearing.
Subscription, license and services, side by side
The subscription model is easier to see next to the two models it replaced. This is the shape, not a verdict; plenty of good businesses run on the other two columns.
| Subscription (SaaS) | Perpetual license | Services | |
|---|---|---|---|
| When the money arrives | A little every month, for as long as the customer stays | Mostly up front, plus optional maintenance | As hours are worked |
| Cost to deliver one more customer | Low: hosting and support, so gross margin of 70% to 80% or more | Low once built, but the vendor does not run the software | High: people’s time, so gross margin of 30% to 50% is common |
| What makes it grow | Retention and expansion of existing customers | New sales every period, because the old ones are paid | More people billing more hours |
| Biggest risk | Churn and the cash gap before CAC is paid back | Replacement cycles and upgrades that customers skip | Idle staff, and key people leaving |
| How it is valued | A multiple of recurring revenue | A multiple of profit | A multiple of profit, usually lower |
The gross margin ranges are the shape of the two models, not figures from a filing; the one sourced data point above is Salesforce’s 77.7%. The valuation row explains the obsession with ARR: a subscription business is priced on revenue it is expected to keep, so the quality of that revenue, meaning churn and expansion, moves the price more than this quarter’s sales do.
Common mistakes
- Counting bookings as revenue. A signed $12,000 annual contract is $1,000 of revenue a month for 12 months, not $12,000 today, even if the cash arrived up front. Why it happens: the cash is in the bank. Instead: keep three lines, bookings, revenue and cash, and never let one stand in for another.
- Ignoring churn in the first-year projection. A forecast that adds 10 customers a month and never subtracts any ends the year at 220 customers instead of 171. Why it happens: a new company has no churn data yet. Instead: assume a rate (2% to 3% monthly is a common starting assumption for small-business products), and replace it with your own number as soon as you have six months of data.
- Comparing a SaaS margin with a services margin. A consultancy with 40% gross margin and a SaaS product with 75% are not in the same business, and bundling them in one plan hides which one is working. Why it happens: many SaaS companies start as agencies. Instead: report the two margins separately, and keep implementation hours out of the subscription line.
- Spending on acquisition before the payback math works. With a 15-month payback and 3% churn, every dollar of acquisition takes over a year to come back. Doubling the sales budget doubles the cash hole before it doubles anything else. Why it happens: growth looks like progress. Instead: compute payback and LTV to CAC from your own numbers first, then decide how fast to open the tap.
Sources
- Salesforce, Inc., Annual Report on Form 10-K for the fiscal year ended January 31, 2026, filed with the SEC: total revenues $41,525 million, subscription and support revenues $39,388 million, cost of revenues $9,270 million, gross profit $32,255 million; subscription and support approximately 95% of total revenues in fiscal 2026. The 77.7% gross margin is SaaSCron’s arithmetic from those lines.
- Metric definitions follow the SaaSCron style guide glossary (MRR, ARR, churn, CAC, gross margin, LTV).
In three sentences
A SaaS business earns a little from each customer every month, keeps most of it because software is cheap to deliver, and grows only when new customers outrun the ones who cancel. In the example, a company that grew MRR by 60% in a year still ended it $4,360 behind, because each customer costs $600 to win and takes 15 months to pay that back. Churn is the lever that changes everything: cutting it from 3% to 2% a month raises lifetime value per customer from about $1,333 to $2,000 without touching price or sales spend.
