Revenue forecasting for an early-stage business is part science, part informed storytelling. Investors and operators alike know that any single-point forecast ("we'll hit $2M ARR next year") is almost certainly wrong in the specific number — the real value of forecasting comes from understanding the range of plausible outcomes and the key assumptions driving each scenario.

Monthly Recurring Revenue (MRR) is the predictable, repeating monthly revenue from active subscriptions — explicitly excluding one-time fees, setup charges, or non-recurring services. Annual Recurring Revenue (ARR) simply annualizes that figure. These metrics matter because they strip out the noise of one-time revenue and reveal the true, compounding growth engine of a subscription business.

Popularized by venture capital firm Bessemer Venture Partners, "T2D3" describes a commonly cited growth trajectory benchmark for top-quartile SaaS companies: Triple, Triple, Double, Double, Double — meaning ARR triples in year one and two of meaningful scale, then doubles for three subsequent years.

Very few companies actually achieve this exact trajectory — it represents a benchmark for elite outliers, not a typical or expected outcome — but it's widely referenced by venture investors as a mental model for what "great" looks like at each stage.

Even a business adding new customers steadily can stagnate or shrink if churn (lost revenue from cancellations and downgrades) outpaces new growth. A SaaS company with $500,000 MRR losing 3% monthly to churn is losing $15,000/month before counting any new sales — meaning it needs to add at least that much in new MRR every single month just to stay flat.

The best-performing SaaS companies achieve what's called negative net revenue churn — where expansion revenue from existing customers (upsells, seat additions, plan upgrades) exceeds the revenue lost from cancellations and downgrades, meaning the existing customer base actually grows in revenue even with zero new customer acquisition. This is considered one of the strongest possible signals of product-market fit and pricing power.

Worked example: a customer paying $200/month with a 2% monthly churn rate has an expected lifetime value of $200 / 0.02 = $10,000. If acquiring that customer cost $2,500 in sales and marketing spend, the LTV:CAC ratio is 4:1 — generally considered healthy. A widely cited rule of thumb suggests an LTV:CAC ratio of at least 3:1 for a sustainable SaaS business; ratios below 1:1 mean the company is losing money on every customer acquired, before even accounting for fixed operating costs.

Rather than a single forecast number, build bear, base, and bull cases by varying your key assumptions: new customer acquisition rate, churn rate, and average revenue per account. This forces explicit acknowledgment of uncertainty and gives investors (and yourself) a realistic range rather than false precision.