The SaaS magic number answers one blunt question that decides whether you should spend more or spend less: for every euro you put into sales and marketing, how much new recurring revenue comes back? It is the number an investor reads in thirty seconds to judge whether your growth engine is efficient — and the number you should read yourself before you approve a bigger budget.
Most definitions online stop at the formula. The part that actually changes a decision is the one they skip: what a healthy result looks like, why the same result can be a trap, and how the magic number talks to your CAC payback. That is what you get here.
What the SaaS magic number measures
The magic number is a measure of sales efficiency at the company level. It sits one floor above the metrics you use to judge a single deal or channel — CAC, LTV/CAC and payback answer "does it pay off to bring this customer this way?". The magic number zooms out and asks the same question about the whole engine: is the entire go-to-market machine turning spend into revenue?
That is why it matters most at two moments: when you are about to hit the accelerator, and when you are raising a round. Both come down to the same bet — that pouring more money into acquisition produces proportionally more ARR, not just more burn.
The formula, quarter by quarter
The formula is deliberately simple:
Magic number = new net ARR this quarter ÷ sales & marketing spend of the previous quarter
Two details do all the work. It uses new net ARR — the recurring revenue you added after subtracting churn and contraction, not gross bookings. And it lags the spend by one quarter, because the money you spent in Q1 is what produced the revenue that showed up in Q2.
Walk it through with a worked example. Take Flowdesk, a B2B SaaS startup:
- End of Q1: ARR is €600,000.
- Q1 sales & marketing spend: €50,000.
- End of Q2: ARR is €645,000.
- New net ARR in Q2: €645,000 − €600,000 = €45,000.
Now divide the new ARR by the previous quarter's spend:
€45,000 ÷ €50,000 = 0.9
Flowdesk's magic number is 0.9. Every euro of Q1 spend brought back 0.90 of new annual recurring revenue — and because ARR recurs year after year, that spend keeps paying long after the quarter closes. As you will see in the next section, 0.9 clears the healthy line comfortably, which means the honest reading is: press.
Calculate your magic number
Enter your two numbers and the calculator returns your magic number and which band you land in.
Run your numbers
Standard quarterly form: (ARR_q − ARR_q_prev) × 4 / (SM_spend_prev_q × 4); the ×4 annualization cancels, so it reduces to the book's quarterly ratio — e.g. 45000 / 50000 = 0.9.
The benchmark: what a good magic number looks like
Here is where a single number becomes a decision. The healthy bands from the book's cheat sheet (> 0.75 accelerate · < 0.5 stop) split the outcome into three actions:
- Above the upper band — accelerate. Your spend is converting into revenue efficiently. This is the green light to invest more: more budget should produce proportionally more ARR.
- Below the lower band — stop. More spend is not the answer. The failure is upstream — in your CAC, your conversion or your positioning — and adding budget just burns it faster. Fix the engine before you feed it.
- In between — tune, then decide. The engine works but leaks efficiency. Repair the weak link before you pour in more.
Treat the band as a place to look, not a verdict. A magic number below the line does not tell you what is broken; it tells you the problem is in acquisition efficiency rather than in spending too little — which is exactly the opposite of what the pressure to "grow faster" pushes you to do. HubSpot learned this the hard way with its sales product: stuck in a middle band where a plan was too expensive to sell self-serve yet too cheap to fund a sales team, the fix Brian Balfour landed on was counterintuitive — they raised the price until one engine finally paid off, and only then did growth take off. The magic number pointed at the engine, not at the budget.
Magic number and CAC payback: the same question, two lenses
The magic number and CAC payback are two views of one idea — how efficiently you buy growth. The magic number reads it as a ratio (ARR per euro spent); payback reads it as time (how many months to recover the cost of a customer). A strong magic number usually travels with a short payback, and a healthy LTV/CAC ratio (≥ 3:1) underneath both.
But the second edition of the book adds a nuance that most benchmark tables miss: the healthy payback band moves with your sales motion. A self-serve product should recover its cost fast; a product-led-with-sales motion can carry a longer payback; and true enterprise, with its long contracts and high expansion, tolerates the longest of all (see < 12 months for the bands by motion). The mistake is applying a single "good payback" number across a self-serve tool and an enterprise platform as if they lived by the same clock. They do not — and neither does the magic number you should expect from each.
There is one more filter the magic number ignores and you must not: payback has to fit inside the client's runway. A startup with eight months of cash cannot afford a channel that takes twelve to pay back, however "healthy" the ratio looks — it runs out of money before the investment returns. Always ask about the cash before you recommend accelerating.
The false positives: growth you cannot bank
A high magic number is not automatically good news. Read it alone and you can be fooled twice.
The leaking bucket. A strong magic number paired with weak retention means you are acquiring efficiently to fill a bucket that drains from the bottom. You are buying new customers well and losing old ones just as fast — the ARR looks like it is growing, but net of churn the engine is bleeding. This is why the magic number is read together with net revenue retention and the quick ratio, never on its own.
Growth bought with discounts. If the quarter's new ARR was won by slashing price, the magic number flatters you. Discounting to close inflates the numerator today and anchors the customer to a lower figure forever — you booked revenue you cannot repeat and cannot raise. Always compute the magic number on net, real ARR, not gross bookings, or the metric "adds up" while the engine quietly loses margin.
The discipline is the same one that runs through every unit-economics decision: no single ratio is a verdict. The magic number tells you whether to press or stop; retention and margin tell you whether the growth you are pressing on is worth keeping.
Frequently asked questions
What is a good SaaS magic number?
Use the healthy bands (> 0.75 accelerate · < 0.5 stop) as a traffic light: above the upper band, your spend converts efficiently and you can invest more; below the lower band, the problem is acquisition efficiency and more budget only burns faster; in between, tune before you scale. Read it as a place to investigate, not a final grade.
How do you calculate the SaaS magic number?
Divide the new net ARR you added this quarter by the sales and marketing spend of the previous quarter. Use net ARR (after churn and contraction), lag the spend by one quarter, and measure on real revenue rather than discounted bookings.
Why lag sales and marketing spend by one quarter?
Because the money you spend now produces revenue later. Sales cycles, onboarding and ramp mean the spend in one quarter shows up as ARR in the next. Matching this quarter's revenue to this quarter's spend understates the true efficiency of a working engine.
Is a high magic number always good?
No. A high magic number with weak retention means you are acquiring efficiently into a leaking bucket, and a high magic number built on discounts is revenue you cannot repeat. Read it alongside net revenue retention and gross margin, never in isolation.
Mario Hernández is a GTM consultant and the founder of creactia, where he runs go-to-market for B2B software teams. He is the author of Go-To-Market: from zero to specialist, the field manual this guide draws on — including the healthy bands and the by-motion payback nuance covered above.
If these numbers look wrong for your startup, that diagnosis is exactly what our GTM audit does: we read your magic number, payback and retention together and tell you where the engine is really leaking.