Runway Planning: 18-Month Rule and Fundraise Timing (2026)

Runway Planning: How Much Cash to Raise and When to Start the Next Round

Runway planning is not spreadsheet math — it's a strategic decision about how much dilution to take and how much time to buy between milestones. Get it wrong and you fundraise from weakness.

The 18-month rule

Raise enough for 18–24 months of runway. Under 18 you'll be back fundraising before the milestones from this round have played out. Over 24 you take unnecessary dilution and slow decision-making.

When to start the next round

Start with 9 months of runway remaining. Fundraises take 3–6 months from first meeting to wire. You want to close with at least 3 months of runway left as insurance against slippage.

Milestone-driven planning

Work backward from the milestones that unlock the next round. What ARR, growth rate, or product proof does a Series B require? What does your monthly burn need to be to reach that with 6 months of buffer? That's your round size.

Two scenarios always

Build a base case and a downside case. Downside assumes 30% slower growth and 20% higher burn. If the downside case still gets you to the next round with 6 months of runway, the raise is properly sized.

The bridge round trap

Bridges signal that the previous round was undersized or the plan slipped. Existing investors often price them punitively. Better to raise a full round with proper structure than a bridge with anti-dilution baggage.

Frequently asked questions

Should I raise more than 24 months of runway?

Rarely. Extra dilution isn't worth extra time unless you have a specific 3-year milestone that justifies it (regulatory, capital-intensive infrastructure).

What if I only have 4 months of runway left?

You're in bridge territory. Talk to existing investors first — they know your business and can move fastest.

Does the 18-month rule apply at seed?

Yes, though seed rounds often fund 12–18 months to a Series A milestone.

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