Most early-stage SaaS founders check their bank balance and call it runway. That's a mistake that leads to bad hiring decisions, missed fundraising windows, and surprises that shouldn't be surprises.
Your bank balance tells you how much cash you have right now. Runway tells you how long that cash will last given your current and planned spending. Those are two very different numbers, and conflating them is one of the most common financial errors at the seed and Series A stage.
What runway actually is
Runway is the number of months you can operate before you run out of cash. The basic formula is straightforward: divide your current cash balance by your monthly net burn rate. If you have $600,000 in the bank and you're burning $50,000 per month, you have 12 months of runway.
But that calculation only works if your burn rate is flat — and it almost never is. The moment you hire someone, your burn rate increases. The moment a customer churns, your revenue drops and your net burn goes up. Runway is a moving target, not a static number.
The three inputs that actually matter
Accurate runway forecasting requires three things: your starting cash position, your projected monthly burn (not your current burn), and your projected monthly revenue. Most founders get the first one right and estimate the other two poorly.
Projected burn is where the bank balance trap hits hardest. You look at last month's expenses, assume they'll stay roughly the same, and divide into your cash. But if you're planning to hire two engineers in Q2, your burn rate in month four is going to be $20,000–$30,000 higher than it is today. That hiring plan needs to be in your runway model, not just in your head.
Why the hiring plan changes everything
Headcount is the largest expense for most SaaS companies, and it's also the most predictable. You know when you're planning to hire, roughly what those roles will cost, and how long it takes to ramp a new employee to full productivity. That information belongs in your financial model.
When you build runway with a staffing plan baked in, you get a much more honest picture. A company with $600,000 in the bank and a plan to hire four people over the next six months might have eight months of runway, not twelve. That's a fundraising timeline, not a comfortable cushion.
The right way to think about it
Treat runway as a forecast, not a calculation. Update it every month when you close your books. When you make a new hire, model the impact immediately. When a customer churns, recalculate. The goal is to never be surprised by your own cash position.
Horizon's financial model keeps your runway calculation live — it updates automatically as you adjust your staffing plan, revenue assumptions, and expense inputs. The dashboard shows you runway in months alongside your burn rate and cash position so the relationship between those numbers is always visible.
Your bank balance is a snapshot. Runway is a forecast. Make sure you're looking at the right number when you're deciding whether to hire.