SaaS economics

SaaS (software as a service) sells ongoing access to software for a recurring fee, usually hosted by the vendor. Spend money upfront to acquire a customer, deliver the product at high gross margin, then earn that customer back over many months while expanding the account. Get retention and expansion right and the business compounds. Get churn wrong and you rebuild the revenue base you already paid to acquire — every year.

This page is the map of that engine. Board vocabulary (ARR, NRR, magic number) lives in SaaS metrics and unit economics.

A cohort — customers who started in the same period — tells the truth. Plot their revenue over time. Logo churn removes customers. Contraction shrinks seats. Expansion grows remaining accounts. Healthy SaaS dips, then flattens or climbs. Unhealthy SaaS slides toward zero: you rented revenue, you did not build a base.

Recurring revenue earns high multiples when growth and retention are healthy because next quarter is mostly already contracted, software gross margins often land in the 70–85% range at scale, and NRR above 100% grows the base without proportional new logos. A services firm resets when the project ends. Same LinkedIn tag; different asset. When churn rises, those multiples compress fast.

Lifetime for crude LTV math is often 1 / annual logo churn. At 10% annual logo churn, lifetime ≈ 10 years. That ignores expansion and changing churn. Do not treat it as truth.

Concepts in this section

When you ship billing or entitlements, you are touching this engine. An off-by-one in seat counting or a broken upgrade path is revenue and trust, not "billing polish."

Know whether a roadmap item is buying new ARR, NRR, or gross margin. Premature enterprise (custom for one logo), discount addiction, fake PLG (freemium users who never activate), and support COGS that scale linearly with logos are the usual ways the engine stalls.

Common mistakes

• Watching total ARR instead of cohort curves. A rising top line can hide a slide to zero on each vintage.
• Paying full CAC for every dollar because the product cannot land small and expand.
• Discounting until ACV cannot support CAC.
• Launching a second SKU before NRR on the first is healthy.

Key takeaways

• SaaS monetizes ongoing access. ACV/ARR measure the run-rate; TCV measures the signed total.
• Land-and-expand plus NRR above 100% is the compounding engine.
• Recurring, high-margin, expandable revenue earns higher multiples than services.
• Cost structure shifts by stage. Early S&M heaviness is normal; later efficiency is required.
• Cohort revenue curves tell the truth. The cash trough is why growth without payback is dangerous.

Further learning

David Skok on the SaaS model, bookings, and churn:

SaaS Metrics 2.0 (David Skok)“If you cannot measure it, you cannot improve it” – Lord Kelvin This article is a comprehensive and detailed look at the key metrics that are needed to understand and optimize a SaaS business. It is a completely updat…For Entrepreneurs Tomasz TunguzVenture capitalist and former Google PM sharing data-driven insights on building successful startups. Join 100K+ founders and investors learning about tech & SaaS.Tomasz Tunguz