SaaS Metrics Every Founder Must Track

Why metrics matter more than intuition

Running a SaaS business without metrics is like flying an aircraft without instruments. You might feel like things are going well, but you have no way to know whether you are climbing, descending, or heading straight for the ground.

The challenge for most founders is not a lack of data. It is the opposite: too many numbers and no clarity on which ones actually matter. Board meetings turn into data dumps. Investor updates become spreadsheets of vanity metrics. And the metrics that would genuinely help you make better decisions sit buried in a CRM or accounting system nobody has time to interrogate.

This guide covers the metrics that actually matter. Not because they look good on a pitch deck, but because they tell you whether your business is healthy, where the problems are, and what to do about them.

Monthly Recurring Revenue (MRR)

MRR is the heartbeat of any subscription business. It represents the normalised monthly revenue from all active subscriptions.

How to calculate it:

Take the total recurring revenue you expect to collect this month from active customers. Exclude one-off fees, professional services, and non-recurring items. If a customer pays £12,000 annually, their MRR contribution is £1,000.

Why it matters:

MRR gives you a clean, comparable measure of revenue momentum month to month. It strips out the noise of annual billing cycles and one-off payments.

The MRR waterfall:

Breaking MRR into its components tells a far richer story:

• New MRR: Revenue from new customers acquired this month
• Expansion MRR: Additional revenue from existing customers (upgrades, additional seats, add-ons)
• Contraction MRR: Revenue lost from existing customers who downgraded
• Churned MRR: Revenue lost from customers who cancelled entirely

If your New + Expansion MRR consistently exceeds Contraction + Churned MRR, you are in a strong position. If not, you have a leaky bucket.

Annual Recurring Revenue (ARR)

ARR is simply MRR multiplied by 12. It is the annualised run rate of your recurring revenue.

When to use MRR vs ARR:

Use MRR for operational decisions and month-to-month trends. Use ARR for strategic conversations: fundraising, board reporting, valuation discussions, and annual planning. Investors think in ARR because it maps naturally to annual growth rates and valuation multiples.

A common mistake is calculating ARR from total recognised revenue rather than recurring subscriptions. If you had £50,000 in professional services last month, that is not ARR. ARR must be genuinely recurring.

Customer Churn Rate

Customer churn measures the percentage of customers you lose over a given period.

How to calculate it:

Monthly Customer Churn = Customers lost during the month / Customers at the start of the month

A SaaS business with 200 customers at the start of the month and 6 cancellations has a 3% monthly churn rate.

Why 3% monthly churn is a crisis:

It sounds small, but compound it. At 3% monthly churn, you lose approximately 31% of your customer base every year. To grow, you need to acquire more than 31% new customers just to stay flat. That is incredibly expensive and unsustainable.

Benchmarks:

• SMB-focused SaaS: 3-5% monthly churn is common (but not healthy)
• Mid-market SaaS: 1-2% monthly churn
• Enterprise SaaS: Less than 1% monthly churn

If your monthly churn exceeds 3%, stop everything else and fix retention. No amount of sales will outrun a leaky bucket.

Revenue Churn (Gross Revenue Retention)

Revenue churn is more important than customer churn because not all customers are equal.

Gross Revenue Retention (GRR):

GRR = (MRR at start of period - Contraction MRR - Churned MRR) / MRR at start of period

This tells you what percentage of revenue you retain from your existing customer base, excluding any expansion. A GRR of 90% means you lose 10% of your revenue annually from downgrades and cancellations alone.

Benchmarks:

• Best-in-class SaaS: GRR above 95%
• Good: 90-95%
• Concerning: Below 85%

If your GRR is below 85%, your product has a fundamental retention problem that no sales team can fix.

Net Revenue Retention (NRR)

NRR is the metric that separates good SaaS businesses from exceptional ones.

How to calculate it:

NRR = (MRR at start + Expansion MRR - Contraction MRR - Churned MRR) / MRR at start

NRR includes expansion revenue. If your customers upgrade, buy add-ons, or add seats, that growth offsets churn. An NRR above 100% means your existing customers are worth more to you this year than last year, even without any new sales.

Why investors love NRR:

An NRR of 120% means that even if you acquired zero new customers, your revenue would still grow 20% year on year. That is a sign of genuine product-market fit, strong pricing power, and a business that compounds.

Benchmarks:

• Best-in-class: NRR above 130% (Snowflake, Datadog territory)
• Excellent: 110-130%
• Good: 100-110%
• Concerning: Below 100%

Customer Lifetime Value (LTV)

LTV estimates the total revenue a customer will generate over their entire relationship with your business.

Simple calculation:

LTV = ARPU / Monthly Churn Rate

Where ARPU is Average Revenue Per User (monthly). If your average customer pays £500/month and your monthly churn rate is 2%, LTV = £500 / 0.02 = £25,000.

More sophisticated calculation:

LTV = ARPU x Gross Margin % / Monthly Churn Rate

This accounts for the fact that not all revenue is profit. A £25,000 LTV at 80% gross margin means £20,000 of actual economic value per customer.

Why it matters:

LTV tells you how much you can afford to spend acquiring a customer and still make money. It is meaningless in isolation. It only becomes powerful when paired with CAC.

Customer Acquisition Cost (CAC)

CAC measures how much you spend to acquire a single new customer.

How to calculate it:

CAC = Total Sales & Marketing spend / Number of new customers acquired

Include everything: salaries, commissions, advertising spend, software tools, event sponsorships, content production. If you spent £120,000 on sales and marketing last quarter and acquired 40 new customers, your CAC is £3,000.

LTV:CAC ratio:

This is the relationship that determines whether your business model works.

• LTV:CAC above 3:1 - Healthy. You generate at least £3 of lifetime value for every £1 spent on acquisition
• LTV:CAC of 1:1 - You are spending £1 to get £1 back. After operating costs, you are losing money on every customer
• LTV:CAC above 5:1 - Either excellent efficiency or underinvestment in growth. You might be leaving money on the table

CAC Payback Period:

CAC Payback = CAC / (ARPU x Gross Margin %)

This tells you how many months it takes to recover your acquisition cost. Below 12 months is strong. Above 18 months is concerning, especially for SMB-focused businesses where customer lifetimes may not be long enough to recover the investment.

The Rule of 40

The Rule of 40 is a simple heuristic used by investors to evaluate the overall health and balance of a SaaS business.

The formula:

Revenue Growth Rate (%) + Profit Margin (%) >= 40

If you are growing at 60% year on year but burning at -30% margin, your score is 30. If you are growing at 25% with 20% margins, your score is 45.

Why it matters:

The Rule of 40 captures the fundamental trade-off between growth and profitability. A business growing at 80% can justify losses. A business growing at 10% cannot.

Benchmarks:

• Score above 40: Strong. You are either growing fast, generating healthy profits, or ideally both
• Score of 20-40: Acceptable for early-stage businesses still finding their stride
• Score below 20: A warning sign. Neither growing fast enough nor profitable enough

Putting it all together

No single metric tells the full story. The power comes from tracking them together and watching the trends:

• MRR + MRR waterfall: Are you growing, and where is the growth coming from?
• Churn + NRR: Are you retaining customers and expanding within them?
• LTV + CAC: Is your unit economics engine working?
• Rule of 40: Are you balancing growth and profitability?

Track these monthly. Report them to your board. Use them to make decisions, not just to look impressive. And if a metric is heading in the wrong direction, act on it immediately. In SaaS, trends compound fast - both the good ones and the bad.

A note on data quality

None of these metrics are useful if the underlying data is wrong. If your MRR includes one-off fees, your churn calculation excludes paused accounts, or your CAC does not include all acquisition costs, you are making decisions based on fiction.

Before worrying about advanced metrics, get the basics right: clean subscription data, accurate revenue recognition, and a chart of accounts that separates recurring from non-recurring revenue. Everything else builds on that foundation.