What Is SaaS (Software as a Service)?
SaaS (Software as a Service) is a software distribution model where applications are hosted in the cloud and delivered to users over the internet on a subscription basis. Instead of purchasing software outright and installing it on local computers, customers pay a recurring fee - monthly or annually - to access the software through a web browser or app. Examples range from small tools like Calendly to enterprise platforms like Salesforce.
Definition: SaaS is a cloud-based software delivery model where a provider hosts and maintains the application, and customers access it via the internet on a subscription basis rather than purchasing and installing it locally.
SaaS vs Other Software Models
Understanding SaaS requires comparing it to other models in the cloud computing stack:
| Model | What You Get | You Manage | Provider Manages | Examples |
|---|---|---|---|---|
| On-Premise | Software license | Everything | Nothing | Microsoft Office (old), SAP on-prem |
| IaaS (Infrastructure) | Virtual machines, storage, networking | OS, runtime, app, data | Hardware, networking | AWS EC2, Google Compute Engine |
| PaaS (Platform) | Development platform | App and data | OS, runtime, infrastructure | Heroku, Google App Engine |
| SaaS (Software) | Complete application | Your data and configuration | Everything else | Slack, Shopify, Zoom |
The fundamental shift with SaaS is that the software vendor takes on the burden of infrastructure, maintenance, updates, and security. Customers get automatic updates, no installation headaches, and access from any device with an internet connection.
How the SaaS Business Model Works
The SaaS business model revolves around recurring revenue. Instead of a large one-time payment, revenue comes in predictable monthly or annual installments. This creates a fundamentally different economic dynamic compared to traditional software:
- High upfront investment - You build the product before generating significant revenue
- Slow initial revenue growth - You earn $50/month per customer, not $500 upfront
- Compounding revenue - Each new customer adds to a growing base of recurring revenue
- Customer retention is everything - Losing existing customers directly reduces revenue, so the product must continuously deliver value
This dynamic means SaaS businesses typically lose money in the early years while building their customer base, then become highly profitable as recurring revenue compounds and acquisition costs are spread over the customer lifetime.
Key SaaS Metrics Every Founder Must Know
MRR (Monthly Recurring Revenue)
MRR is the total predictable revenue your business earns each month from all active subscriptions. If you have 100 customers paying $50/month, your MRR is $5,000. MRR is the single most important number in a SaaS business because it shows the health and trajectory of the business at a glance.
ARR (Annual Recurring Revenue)
ARR is simply MRR multiplied by 12. It normalizes revenue on an annual basis and is the standard metric for SaaS businesses once they pass roughly $1 million in annual revenue. Investors, especially at Series A and beyond, think in terms of ARR.
Churn Rate
Churn measures the percentage of customers (or revenue) lost in a given period. If you start the month with 200 customers and lose 10, your monthly customer churn is 5%. Even small churn rates compound devastatingly: 5% monthly churn means losing nearly half your customers every year. Reducing churn is often more valuable than acquiring new customers.
Net Revenue Retention (NRR)
NRR measures how much revenue you retain from existing customers, including expansions and upsells minus churn and contractions. An NRR above 100% means existing customers are spending more over time - even without acquiring new ones. Top SaaS companies achieve NRR of 110-130% or higher. This is the metric that separates good SaaS businesses from great ones.
Customer Acquisition Cost (CAC) and Lifetime Value (LTV)
CAC is how much you spend to acquire one customer. LTV is how much total revenue that customer generates before they churn. The general benchmark is an LTV:CAC ratio of at least 3:1 - meaning each customer generates three times what it cost to acquire them. Understanding your pricing strategy is essential for optimizing this ratio.