How FDD reads a SaaS target: ARR and MRR, gross and net revenue retention, logo vs revenue churn, the MRR bridge, CAC payback, the rule of 40 and deferred revenue.
The first time an FDD analyst opens a SaaS data room, the temptation is to reach for the familiar tools — revenue by year, gross margin, an EBITDA bridge — and start there. That instinct is exactly wrong. A software-as-a-service business does not really sell revenue; it sells recurring relationships, and the value of the company lives in the durability of those relationships far more than in any single year's P&L. A SaaS target with flat revenue can be a wonderful asset or a dying one, and the income statement alone will not tell you which. The answer lives in a different vocabulary — ARR, MRR, retention, churn, the MRR bridge, CAC payback — and in one deceptively simple question: of the revenue the business had at the start of the year, how much did it still have at the end? Learn to read those metrics, connect them back to the accounting, and you can value a SaaS business the way its buyers actually do.
Everything starts with the recurring base. ARR (annual recurring revenue) is the annualised value of the subscription contracts a business has at a point in time — the run-rate of its recurring revenue if nothing changed. MRR (monthly recurring revenue) is the same idea expressed monthly; ARR is simply MRR × 12.
The critical discipline in SaaS diligence is separating recurring from non-recurring. ARR should capture only genuinely repeating subscription revenue — not one-off implementation fees, professional services, training days or hardware. A management team keen to inflate the headline will happily fold €800k of one-off services into an "ARR" figure. FDD's first job is to strip the base back to what is truly contractual and repeating, which is why this work sits so close to the broader recurring revenue analysis. A euro of true ARR is worth far more than a euro of services revenue, because one repeats by default and the other must be won again from scratch.
Takeaway: ARR is a point-in-time run-rate, not a period's revenue. Confuse the two, or let services leak into it, and every metric downstream is built on sand.
If ARR is the size of the recurring base, retention is its integrity — and it is the single metric that most influences what a SaaS business is worth. There are two retention numbers that matter, and confusing them is the most common error in SaaS diligence.
Gross revenue retention (GRR) measures how much of your starting recurring revenue you keep, before counting any expansion from existing customers. It can never exceed 100%. It is the purest measure of stickiness: strip out upsell entirely, and how much of last year's base is still paying?
Net revenue retention (NRR) measures the same starting cohort including expansion — upsells, cross-sells, seat growth, price rises. NRR can exceed 100%, and when it does it means the existing customer base grew in value even before a single new customer was added. An NRR comfortably above 100% is the hallmark of a high-quality SaaS business, because it means the company grows even if new-logo acquisition stalls.
The gap between them is diagnostic. A business with NRR of 115% but GRR of 82% is expanding fast within its best accounts while quietly bleeding smaller ones — a very different risk profile from a business with 100% NRR and 96% GRR. FDD reports both, always.
Churn is retention's mirror image, and here too the distinction is everything.
Logo churn counts customers lost — the proportion of accounts that left, regardless of size. Revenue churn counts revenue lost — the proportion of MRR that walked out the door. The two can diverge sharply and the divergence is the story.
If a business loses 15% of its logos but only 4% of its revenue, it is shedding small, marginal accounts while retaining the large ones that matter — often perfectly healthy, and cheaper to serve. If it loses 5% of logos but 18% of revenue, it is losing its biggest customers, which is far more dangerous and usually points to a concentration problem worth cross-reading against customer concentration in FDD. Reporting only one churn number hides which of these two very different worlds the target lives in.
The single most powerful artefact in SaaS diligence is the MRR bridge (or "MRR walk"). It decomposes the movement in recurring revenue between two dates into its four component forces, and it exposes the true quality of growth in a way no revenue line ever can.
$$\text{Closing MRR} = \text{Opening MRR} + \text{New} + \text{Expansion} - \text{Contraction} - \text{Churn}$$
Consider a business that grows MRR from €1,000k to €1,150k over a year — a tidy-looking 15% headline. The bridge tells you how.
| Component | MRR movement (€000) | Running MRR (€000) |
|---|---|---|
| Opening MRR | — | 1,000 |
| New logos | +260 | 1,260 |
| Expansion (existing customers) | +90 | 1,350 |
| Contraction (downgrades) | −70 | 1,280 |
| Gross churn (customers lost) | −130 | 1,150 |
| Closing MRR | 1,150 |
From this single table the analyst reads the metrics that matter. Gross revenue retention is (1,000 − 70 − 130) / 1,000 = 80%. Net revenue retention is (1,000 − 70 − 130 + 90) / 1,000 = 89%. The 15% headline growth is being carried entirely by new-logo acquisition of €260k, while the existing base is actually shrinking on a net basis — because expansion of €90k is not covering €200k of contraction and churn. That is a business on a treadmill: it must win ever more new logos just to stand still, and the moment new-logo growth slows, MRR will fall. No revenue line would ever have told you that. The MRR bridge did it in five rows.
A leaky bucket doesn't show up in the revenue trend — it shows up in the MRR bridge. A business can post confident top-line growth while its net retention quietly falls below 100%. That gap between the headline and the bridge is where SaaS diligence earns its keep.
Two more measures round out the picture, both read qualitatively rather than as pass/fail thresholds.
CAC payback asks how many months of gross-margin-adjusted recurring revenue it takes to recover the cost of acquiring a customer. It ties the sales-and-marketing spend to the value it buys.
$$\text{CAC payback (months)} = \frac{\text{Sales & marketing spend to acquire a customer}}{\text{Monthly recurring revenue per customer} \times \text{Gross margin %}}$$
A short payback means the growth engine is efficient — the business recovers its acquisition cost quickly and every new customer turns cash-positive sooner. A long and lengthening payback means growth is being bought at an increasing price, which matters enormously for how much runway and capital the buyer will need to keep the flywheel spinning.
The rule of 40 is the familiar shorthand that a healthy SaaS business should have revenue growth rate plus EBITDA (or free-cash-flow) margin summing to at least 40%. It is a sanity check, not a valuation formula: a business can grow at 60% while burning cash, or grow at 10% while highly profitable, and both can clear the bar. FDD uses it to frame the growth-versus-profitability trade-off, never as a mechanical verdict.
The two measures are best read together. A short CAC payback and a rule-of-40 score comfortably above the line describe a business that is compounding efficiently — it converts sales spend into durable, high-retention revenue and does so without lighting cash on fire. A long CAC payback paired with heavy growth and deep losses describes a business buying its top line, where the whole model rests on new-logo momentum continuing indefinitely. The buyer inherits whichever engine the metrics describe, and the amount of capital they must commit after completion depends directly on which one it is. FDD's role is not to declare the business good or bad on these ratios, but to make the trade-off legible so the deal team can price the runway the target will need.
All of this exists because SaaS diligence genuinely differs from a standard trading-company review. The value sits in a recurring, contracted base rather than in transactional sales; the key metrics are operational rather than purely financial; and the accounting has its own traps. Read alongside the wider revenue quality analysis, the SaaS lens is less about last year's profit and more about the durability and unit economics of the recurring engine.
The most important accounting bridge is deferred revenue. SaaS customers frequently pay annually in advance, so cash arrives long before the revenue is earned. That upfront cash creates a deferred-revenue liability on the balance sheet — an obligation to deliver the service already paid for — which is why it is often treated as a debt-like item in the price mechanism and belongs in the same conversation as net debt in FDD. The mechanics of that classification, and its cash-flow consequences, are drawn out fully in the deferred revenue analysis. A rapidly growing SaaS business can look cash-rich precisely because it is collecting a year of subscriptions upfront — a flattering picture that FDD has to unwind to see the underlying economics. The classification then flows through to the enterprise-to-equity bridge, where getting deferred revenue right or wrong can move the equity price materially.
SaaS questions are increasingly common in Transaction Services interviews as more deals involve software targets. A favourite: "A SaaS company grew revenue 15% last year. Management is thrilled. What would you want to see before you share their enthusiasm?"
A strong answer refuses the headline and reaches for the bridge:
"Fifteen percent revenue growth tells me almost nothing on its own, because it doesn't say where the growth came from. The first thing I'd ask for is an MRR bridge — opening MRR, new, expansion, contraction and churn — so I can see whether the growth is coming from a durable base or from new-logo acquisition papering over a leaky bucket. From that I'd calculate gross and net revenue retention: if net retention is below 100%, the existing base is shrinking and the whole business depends on ever-rising new sales just to stand still. I'd separate logo churn from revenue churn to see whether they're losing small accounts or their biggest ones, and I'd cross-check against customer concentration. Then I'd look at CAC payback to understand whether that new-logo growth is being bought efficiently or at an escalating cost. And I'd strip any one-off services revenue out of ARR, because that isn't recurring. Only once I've seen the bridge and the retention figures would I know whether 15% growth is a sign of a great business or a warning sign in disguise."
That answer works because it treats the revenue number as a question, not an answer, and knows exactly which artefacts turn it into one.
A SaaS business hides its truth in plain sight. The revenue line looks reassuring, the growth rate sounds impressive, and the cash balance flatters — right up until you build the MRR bridge and watch the base leak out one contraction and one lost logo at a time. The craft of SaaS diligence is refusing to be satisfied by the headline: strip the services out of ARR, separate the two retention numbers, split churn between logos and revenue, and follow the deferred-revenue cash back to the liability it really is. Do that, and you stop reading the income statement the target wants you to read, and start reading the recurring engine the buyer is actually paying for. In software deals, that difference is the whole ballgame.
The Transaction Services Interview Programme (€119.99, one-time) includes a full SaaS module: building an MRR bridge from a raw subscription ledger, calculating gross and net revenue retention, splitting logo from revenue churn, assessing CAC payback, and unwinding the deferred-revenue distortion into the equity bridge. Enrol today.
Hundreds of candidates prepared their interviews with this programme. Those who landed the role have one thing in common: they worked the cases before walking into the room.
