SaaS growth is often described in terms of new customers.
But new customer acquisition is only one part of the recurring revenue equation.
A SaaS company's future revenue also depends on:
- How many customers it retains
- How many customers churn
- How much existing customers expand
- How much recurring revenue contracts through downgrades or reduced usage
- How pricing changes over time
That means a useful SaaS forecast should model subscriber growth, churn, and expansion together rather than treating each metric independently.
RunSmart by Projection Genie connects Stripe subscription data with QuickBooks Online financial data so SaaS founders can establish a baseline from historical performance and model how changes in subscriber growth, churn, expansion, pricing, hiring, spending, and other assumptions could affect future revenue, profitability, cash flow, and runway.
This guide explains how to model the core drivers of SaaS recurring revenue and how those drivers work together to shape the financial future of the business.
What Drives SaaS Recurring Revenue Growth?
Recurring revenue growth is driven by both additions and losses.
A simplified formula is:
Ending MRR = Beginning MRR + New MRR + Expansion MRR - Contraction MRR - Churned MRR
This means MRR can change because:
- New customers are added
- Existing customers spend more
- Existing customers spend less
- Customers cancel
The same principle applies to subscriber counts.
A simplified customer formula is:
Ending Subscribers = Beginning Subscribers + New Subscribers - Churned Subscribers
A SaaS company therefore needs to understand both acquisition and retention to forecast growth accurately.
Why Should Subscriber Growth, Churn, and Expansion Be Modeled Together?
These variables interact.
Higher subscriber growth may increase MRR.
Higher churn may offset part or all of that growth.
Expansion revenue may allow the company to continue growing even if new customer acquisition slows.
For example, two SaaS businesses might each add 100 customers per month.
But if Company A loses 20 customers and Company B loses 80, their net growth will be very different.
Similarly, two companies with the same customer count may generate very different MRR if one has strong expansion from existing customers.
Looking at only one metric can therefore give an incomplete view of future recurring revenue.
How Do You Model SaaS Subscriber Growth?
Subscriber growth measures how the customer base changes over time.
A simplified formula is:
Ending Subscribers = Beginning Subscribers + New Subscribers - Churned Subscribers
Suppose a SaaS company begins the month with:
- 1,000 subscribers
- 80 new subscribers
- 30 churned subscribers
Ending subscribers are:
1,000 + 80 - 30 = 1,050
Net subscriber growth is:
50 customers
The net subscriber growth rate is approximately:
50 ÷ 1,000 × 100 = 5%
This shows why gross new customer additions alone are not enough.
The company added 80 customers, but the customer base only grew by 50.
What Is Gross Subscriber Growth?
Gross subscriber growth measures new customers added before subtracting churn.
If a company begins with 1,000 subscribers and adds 80:
Gross Subscriber Growth = 80 ÷ 1,000 × 100 = 8%
But if 30 customers churn, net growth is only 5%.
Gross acquisition therefore explains how quickly the company is adding customers.
Net growth explains how quickly the overall subscriber base is actually growing.
How Do You Model SaaS Churn?
Customer churn measures the percentage of customers lost during a period.
A simplified formula is:
Customer Churn Rate = Customers Lost ÷ Beginning Customers × 100
Suppose a company begins with 1,000 customers and loses 30.
30 ÷ 1,000 × 100 = 3% monthly churn
If the company adds 50 customers in the same month:
Ending Customers = 1,000 + 50 - 30 = 1,020
The company is still growing, but churn has reduced net growth.
How Does Churn Affect Subscriber Growth?
Churn acts as a drag on acquisition.
Suppose a SaaS company adds 60 customers per month.
At 2% churn from a 1,000-customer base:
1,000 × 2% = 20 churned customers
Net growth:
60 - 20 = 40 customers
At 5% churn:
1,000 × 5% = 50 churned customers
Net growth:
60 - 50 = 10 customers
The company acquires the same number of new customers in both cases, but net growth falls from 40 to 10 customers.
That is a 75% reduction in net customer growth caused entirely by higher churn.
What Is Expansion Revenue?
Expansion revenue is additional recurring revenue generated from existing customers.
Expansion may come from:
- Upgrading to a higher-priced plan
- Adding seats
- Increasing usage
- Purchasing additional recurring features
- Increasing contract value
- Moving from monthly to higher-value packages
Expansion allows MRR to grow without requiring the company to acquire another customer.
How Do You Calculate Expansion MRR?
Expansion MRR is the additional monthly recurring revenue generated from existing customers during a period.
Suppose a company has:
- 100 customers who each upgrade by $20 per month
Expansion MRR is:
100 × $20 = $2,000
If beginning MRR was $100,000:
Expansion Rate = $2,000 ÷ $100,000 × 100 = 2%
Expansion can partially or completely offset revenue lost through churn and contraction.
What Is Contraction Revenue?
Contraction is the opposite of expansion.
It occurs when an existing customer continues subscribing but generates less recurring revenue.
Examples include:
- Downgrading plans
- Removing seats
- Reducing usage
- Negotiating lower pricing
Suppose 50 customers reduce their subscriptions by $20 per month.
Contraction MRR is:
50 × $20 = $1,000
That $1,000 reduces recurring revenue even though those customers have not fully churned.
How Do Expansion and Churn Work Together?
Expansion and churn both affect the value of the existing customer base.
Suppose a SaaS company begins with:
- $100,000 MRR
- $5,000 expansion MRR
- $2,000 contraction MRR
- $4,000 churned MRR
Ending recurring revenue from the existing customer base is:
$100,000 + $5,000 - $2,000 - $4,000 = $99,000
The existing customer base has declined slightly.
Now suppose expansion MRR increases to $8,000:
$100,000 + $8,000 - $2,000 - $4,000 = $102,000
The existing customer base is now producing more recurring revenue than it did at the beginning of the period.
This interaction is one of the reasons Net Revenue Retention is so useful.
What Is Net Revenue Retention?
Net Revenue Retention, or NRR, measures how recurring revenue from an existing customer base changes after accounting for expansion, contraction, and churn.
A simplified formula is:
NRR = (Beginning MRR + Expansion MRR - Contraction MRR - Churned MRR) ÷ Beginning MRR × 100
Using the previous example:
- $100,000 beginning MRR
- $8,000 expansion
- $2,000 contraction
- $4,000 churn
NRR is:
($100,000 + $8,000 - $2,000 - $4,000) ÷ $100,000 × 100
NRR = 102%
An NRR above 100% means the existing customer base is growing in recurring revenue even before new customers are added.
How Does New MRR Fit Into the Model?
New MRR represents recurring revenue from newly acquired customers.
Suppose a company adds:
- 50 new customers
- $100 average monthly recurring revenue per new customer
New MRR is:
50 × $100 = $5,000
If the company also has:
- $3,000 expansion MRR
- $1,000 contraction MRR
- $2,000 churned MRR
Net MRR change is:
$5,000 + $3,000 - $1,000 - $2,000 = $5,000
If beginning MRR is $100,000:
Ending MRR = $105,000
What Is Net New MRR?
Net New MRR summarizes the net recurring revenue added during a period.
A simplified formula is:
Net New MRR = New MRR + Expansion MRR - Contraction MRR - Churned MRR
Using the example above:
$5,000 + $3,000 - $1,000 - $2,000 = $5,000 Net New MRR
Net New MRR is useful because it shows how all recurring revenue gains and losses combine.
How Do You Forecast Subscriber Growth Over Time?
A subscriber forecast repeats the customer growth calculation for each future period.
Suppose a SaaS company begins with:
- 1,000 customers
- 5% monthly new subscriber growth
- 3% monthly customer churn
For a simplified example:
New customers:
1,000 × 5% = 50
Churned customers:
1,000 × 3% = 30
Ending customers:
1,000 + 50 - 30 = 1,020
The next month begins with 1,020 customers.
If the same assumptions continue:
New customers:
1,020 × 5% = 51
Churned customers:
1,020 × 3% = 30.6
The subscriber base continues compounding.
This repeated process creates the future customer trajectory.
How Do You Forecast Expansion Revenue?
Expansion can be modeled as either:
- A percentage of recurring revenue
- An expected dollar amount
- A percentage of customers upgrading
- Expected seat or usage growth
- Plan-specific upgrade assumptions
Suppose a company has $100,000 in beginning MRR and historically generates 2% monthly expansion.
Expected expansion MRR:
$100,000 × 2% = $2,000
If MRR grows to $150,000 and the expansion rate remains 2%:
$150,000 × 2% = $3,000
Expansion therefore compounds as the recurring revenue base grows.
How Do You Model Subscriber Growth, Churn, and Expansion Together?
The three variables can be combined into one recurring revenue model.
Suppose a company begins with:
- 1,000 customers
- $100 average MRR per customer
- $100,000 beginning MRR
- 50 new customers per month
- 3% monthly customer churn
- 2% monthly expansion
- 1% monthly contraction
Customer churn:
1,000 × 3% = 30 customers
Ending customers:
1,000 + 50 - 30 = 1,020
New MRR:
50 × $100 = $5,000
Expansion MRR:
$100,000 × 2% = $2,000
Contraction MRR:
$100,000 × 1% = $1,000
If churned customers also average $100 per month:
Churned MRR:
30 × $100 = $3,000
Ending MRR becomes:
$100,000 + $5,000 + $2,000 - $1,000 - $3,000 = $103,000
The company ends with:
- 1,020 subscribers
- $103,000 MRR
That gives a more complete picture than simply saying the company added 50 customers.
How Do Different Growth Drivers Produce Different Outcomes?
Two SaaS companies can reach similar MRR growth with very different underlying economics.
A company driven primarily by new customer acquisition may need continuous sales and marketing investment.
A company with strong expansion and low churn may generate more growth from its existing customer base.
Understanding the source of growth matters when forecasting future financial performance.
How Do You Create SaaS Growth Scenarios?
Scenario modeling allows founders to change the assumptions behind subscriber growth, churn, and expansion.
For example:
Each scenario produces a different future MRR and customer trajectory.
The resulting revenue forecast can then be connected to the broader company financial model.
Example: Faster Subscriber Growth With Higher Churn
Suppose a SaaS company is considering increasing its marketing investment.
The company expects:
- Subscriber growth to rise from 5% to 8%
- Churn to rise from 3% to 4%
- Expansion to remain at 2%
The faster acquisition rate may produce stronger gross growth.
But higher churn reduces the number of customers retained.
A useful model compares the net result rather than assuming more acquisition automatically leads to proportionally higher recurring revenue.
Example: Slower Acquisition With Better Retention
Now suppose a different scenario produces:
- 4% subscriber growth
- 1.5% churn
- 3% expansion
The company is acquiring customers more slowly.
But it is retaining more customers and generating more revenue from the customers it keeps.
Over time, this scenario could produce a competitive or even stronger recurring revenue trajectory despite lower new customer acquisition.
The exact result depends on the starting base and how each assumption compounds.
Can Expansion Offset Churn?
Yes.
Expansion can offset some or all recurring revenue lost through churn and contraction.
Suppose a company has:
- $100,000 beginning MRR
- $7,000 expansion MRR
- $2,000 contraction MRR
- $5,000 churned MRR
The existing customer base ends at:
$100,000 + $7,000 - $2,000 - $5,000 = $100,000
Expansion has fully offset the revenue lost through churn and contraction.
If expansion rises above $7,000, the existing customer base begins growing before any new customer acquisition is included.
Can SaaS Grow Without Adding New Customers?
Yes, at least for a period, if expansion revenue from existing customers exceeds contraction and churn.
Suppose:
- Beginning MRR = $100,000
- New MRR = $0
- Expansion MRR = $10,000
- Contraction MRR = $2,000
- Churned MRR = $5,000
Ending MRR is:
$100,000 + $0 + $10,000 - $2,000 - $5,000 = $103,000
MRR has grown 3% even though no new customers were added.
This demonstrates how valuable expansion can be in a SaaS model.
Can a SaaS Company Add Customers but Still Shrink Revenue?
Yes.
If the customers leaving are worth more than the customers joining, customer count can rise while MRR falls.
Suppose:
- 20 customers churn at $500 per month
- 50 new customers join at $100 per month
Churned MRR:
20 × $500 = $10,000
New MRR:
50 × $100 = $5,000
Customer count increases by 30.
But MRR falls by:
$5,000
This is why customer growth and revenue growth should be analyzed together.
Why ARPU and ARPA Matter in SaaS Forecasting
Average Revenue Per User or Average Revenue Per Account helps translate customer counts into recurring revenue.
A simplified formula is:
ARPU = MRR ÷ Active Customers
Suppose:
- MRR = $120,000
- Active customers = 1,000
ARPU is:
$120,000 ÷ 1,000 = $120
If subscriber count grows but ARPU falls because more customers choose lower-priced plans, revenue growth may be weaker than customer growth suggests.
Similarly, rising ARPU can amplify recurring revenue growth.
How Do Pricing Changes Affect Subscriber Growth and Expansion?
Pricing can affect several forecast drivers simultaneously.
A higher price may:
- Increase revenue per customer
- Increase churn
- Slow customer acquisition
- Increase expansion revenue
- Cause downgrades
- Change plan mix
A lower price may:
- Accelerate acquisition
- Improve retention
- Reduce revenue per customer
Pricing should therefore be modeled alongside subscriber growth, churn, and expansion rather than as a separate calculation.
How Do These SaaS Metrics Affect Cash Flow?
Subscriber growth, churn, and expansion affect the future recurring revenue base.
That revenue then influences cash inflows.
But cash flow also depends on expenses.
For example, faster subscriber growth might require:
- Higher marketing spending
- More sales employees
- More customer support staff
- Higher infrastructure costs
A company may therefore grow MRR while continuing to burn cash.
This is why recurring revenue forecasts should eventually connect to broader financial forecasts.
How Do These Metrics Affect SaaS Runway?
If stronger retention and expansion increase revenue without proportionally increasing expenses, cash burn may decline and runway may improve.
If aggressive subscriber growth requires large increases in hiring and marketing, cash burn may increase even as MRR grows.
Runway depends on the resulting cash flow, not on subscriber growth alone.
A simplified formula is:
Runway = Available Cash ÷ Monthly Net Cash Burn
A forward-looking forecast is more useful because monthly cash burn may change as the recurring revenue base and expense structure change.
Which SaaS Growth Metrics Should Founders Monitor Together?
No single SaaS metric tells the entire growth story.
Together, these metrics show how effectively a SaaS company is acquiring customers, retaining them, and increasing the value of the existing customer base.
How RunSmart Models Subscriber Growth, Churn, and Expansion Revenue
RunSmart by Projection Genie combines Stripe subscription data with QuickBooks Online financial data to give SaaS founders a forward-looking view of both the recurring revenue engine and the broader financial business.
Stripe provides historical information about:
- Subscribers
- Subscription growth
- Churn
- Expansion
- Contraction
- Pricing
- Recurring revenue
RunSmart uses that historical performance to establish a baseline forecast.
Founders can then model changes to:
- Subscriber growth
- Churn
- Expansion revenue
- Pricing
- Hiring
- Spending
- Financing
- Other financial assumptions
RunSmart recalculates the forecast so founders can evaluate how those changes could affect:
- MRR
- ARR
- Revenue
- Profitability
- Cash flow
- Financial health
- Runway
This allows founders to see how changes in SaaS operating metrics could flow through to the financial future of the company.
Why SaaS Growth Should Be Modeled as a System
Subscriber growth, churn, and expansion are often displayed as separate metrics.
But financially, they operate as one system.
New subscribers increase the recurring revenue base.
Churn removes customers and recurring revenue.
Expansion increases the value of existing customers.
Contraction reduces that value.
Pricing influences all of them.
The future MRR trajectory is the result of how these variables interact.
That is why SaaS forecasting should not assume that faster customer acquisition alone creates a stronger business.
The more useful question is:
How do acquisition, retention, and expansion work together to shape future recurring revenue and financial performance?
Frequently Asked Questions
How do you model SaaS subscriber growth?
Start with beginning subscribers, add expected new customers, and subtract expected churned customers for each future period. The resulting ending customer count becomes the starting point for the next period.
What is the formula for net subscriber growth?
A simplified formula is Ending Subscribers = Beginning Subscribers + New Subscribers - Churned Subscribers.
How does churn affect SaaS growth?
Churn reduces the number of customers retained and therefore reduces net subscriber growth. Higher churn can offset much of the benefit of new customer acquisition.
What is expansion revenue?
Expansion revenue is additional recurring revenue generated from existing customers through upgrades, additional seats, increased usage, or other increases in recurring spending.
What is contraction revenue?
Contraction revenue is recurring revenue lost when existing customers downgrade, remove seats, reduce usage, or otherwise spend less without fully canceling.
How do you calculate Net New MRR?
A simplified formula is New MRR + Expansion MRR - Contraction MRR - Churned MRR.
What is Net Revenue Retention?
Net Revenue Retention measures how recurring revenue from an existing customer base changes after expansion, contraction, and churn.
Can expansion revenue offset churn?
Yes. If expansion revenue is large enough, it can offset some or all recurring revenue lost through churn and contraction.
Can a SaaS company grow MRR without adding new customers?
Yes. If expansion revenue from existing customers exceeds revenue lost from churn and contraction, MRR can increase even without new customer acquisition.
Can customer count grow while MRR declines?
Yes. This can happen if higher-value customers churn while lower-value customers are added.
Should SaaS founders model growth and churn together?
Yes. Gross customer acquisition does not show how quickly the overall customer base is actually growing. Modeling churn alongside acquisition provides a more realistic net growth forecast.
Can RunSmart model subscriber growth, churn, and expansion?
Yes. RunSmart allows SaaS founders to model these recurring revenue drivers within financial scenarios and compare how different assumptions could affect future MRR and broader financial performance.
Can RunSmart show how SaaS growth affects cash flow and runway?
Yes. Because RunSmart combines Stripe subscription data with QuickBooks Online financial data, changes in recurring revenue assumptions can be evaluated alongside profitability, cash flow, financial health, and runway.
Turning SaaS Growth Metrics Into a Forward-Looking Revenue Model
Subscriber growth tells you how quickly customers are being added.
Churn tells you how quickly they are leaving.
Expansion tells you whether the customers who remain are becoming more valuable.
None of these metrics should be viewed in isolation.
Together, they determine how the recurring revenue base evolves over time.
RunSmart connects Stripe subscription data with QuickBooks financial data to establish a baseline and lets SaaS founders model how different combinations of growth, churn, expansion, pricing, and broader business decisions could affect the company's financial future.
Instead of asking only:
How many new customers are we adding?
Founders can ask:
How are acquisition, retention, and expansion working together to determine where our business is heading?
