Bridge Rounds Explained: When and How to Raise One

What Is Driver-Based Revenue Forecasting?

A revenue forecast is a projection of the money your business will earn over a defined future period. There are two ways to build one:

Top-down forecasting starts with the total addressable market and works down to a market share assumption: “The UK B2B software market is worth £10 billion. If we capture 0.1%, we generate £10 million in revenue.” Useful for sizing the opportunity, useless for operational planning. Investors have heard thousands of 0.1% market share projections and are rightly sceptical.

Bottom-up, driver-based forecasting starts with the specific activities that generate revenue: “We have capacity to run 20 outbound sales conversations per week. Our conversion rate is 10%. Our average contract value is £12,000 per year. That gives us 2 new customers per week, or roughly 100 new customers per year, generating £1.2 million in new ARR.” Every assumption in that chain is testable, improvable, and explainable.

Driver-based forecasting is also the input layer for your 3-statement model — your revenue drivers feed the income statement, which integrates with the balance sheet and cash flow statement.

Why a Revenue Forecast Startup Needs a Different Approach

Established businesses forecast revenue by extrapolating historical data. Startups do not have historical data. The entire forecast must be built on forward-looking assumptions rather than trend lines. A driver-based model built on transparent assumptions is actually more useful to an early-stage investor than a statistical extrapolation, because it makes the business logic explicit and discussable.

The Core Framework: Identify Your Revenue Drivers

What Is a Bridge Round, Exactly?

A bridge round is financing raised between two priced equity rounds, structured almost always as a SAFE or convertible note rather than a new priced round with its own valuation negotiation. Its purpose is specific: get the company to a value-inflection milestone, a revenue target, a product launch, a key hire, so the next round can be raised from a position of strength rather than under time pressure. Bridges have become a normal, even routine, part of the fundraising landscape rather than a last resort; many well-regarded companies raise one or more bridges between primary rounds as a deliberate part of their capital strategy, not as a sign of distress. A bridge is not the same as a down round; a down round is a new priced equity round at a lower valuation than the last one, while a bridge defers the pricing question entirely until the next priced round.

When Should You Raise a Bridge Instead of Waiting for a Priced Round?

The clearest signal: fewer than six months of runway remaining while your metrics are not yet where the next round typically prices. Other common triggers include a broader market pullback that's made new investors more cautious regardless of your own performance, needing four to nine more months to hit a specific milestone that would meaningfully change your valuation, or existing investors proactively offering support without wanting to run a full new-round process.

A simple decision rule: if your runway shows under six months remaining and your trailing growth rate or Rule of 40 score is not yet where the next stage typically prices, a bridge is usually the better move over rushing into an underpriced priced round.

How Big Should a Bridge Round Be?

Formula: Bridge size = Target months of runway extension x Net monthly burn x Buffer factor (1.2 to 1.3).

Worked example: a company burning $80,000 per month net, targeting 12 months of additional runway, with a 1.25x buffer for slippage, needs roughly $1.2M ($80,000 x 12 x 1.25). Undersizing a bridge is one of the most common mistakes founders make, since it just recreates the same cash crunch a few months later, this time with less goodwill from investors. Model at least two scenarios side by side, a base case and a slower-growth case, since a bridge sized only to your optimistic plan can leave you short if the milestone takes longer to hit than expected, which is a common outcome even for well-run companies. Run your own numbers through the runway and burn calculator before setting a target size.

What Terms Are Typical for a Bridge SAFE or Note?

Bridge terms are usually a bit tighter than a first-round SAFE, reflecting the shorter time horizon and higher perceived risk:

• Discount: Typically 10% to 20% off the next priced round, sometimes slightly below the 15% to 20% standard for a first SAFE.
• Valuation cap: Usually set at or modestly above the last priced round rather than freshly negotiated, since a full valuation negotiation defeats the purpose of moving quickly.
• Most Favored Nation (MFN) clause: Common in bridges, protecting early bridge investors if a later investor in the same bridge gets better terms.
• Interest rate (if a note): Typically 4% to 8% simple interest, non-cash pay, accruing until conversion.

Because a bridge often stacks on top of SAFEs or notes already outstanding, understand exactly how multiple SAFEs layer and convert together before setting terms, since the combined dilution at conversion can surprise founders who modeled each instrument in isolation.

Who Should You Ask First: Existing Investors or New Ones?

Insider-led bridges are common and often move faster, since existing investors already have full context and diligence friction is lower. But an all-insider bridge with zero new outside participation can itself read as a caution signal to future investors unless it's clearly explained as a deliberate, milestone-based decision rather than a sign no one else would fund the company. Bringing in even one or two new investors alongside existing ones adds outside validation and is generally worth the extra coordination effort. Ask your existing investors directly and early whether they're inclined to participate before spending time building a full new-investor pipeline for what is meant to be a fast process; a quick informal read from your board and lead investor tells you which path to pursue within days, not weeks.

How Does a Bridge Affect Your Cap Table and Next Round?

Multiple SAFEs and notes at different caps convert simultaneously at the next priced round, and the cumulative dilution can be a real surprise if it isn't modeled ahead of time. Map the full stack against your cap table before you set bridge terms, not after. A bridge priced at a very low cap can also pressure your next 409A valuation downward, and if the implied price is meaningfully below your last priced round, it can function economically like a down round even though it's structured as a SAFE, so treat the cap-setting decision with the same seriousness you would a priced round's valuation.

How Do You Pitch a Bridge Round to Investors?

Be direct about the reason: frame it around the specific milestone the bridge buys, not simply "we're running low on cash." Show the exact math behind the ask using your financial model so investors can see precisely what the capital extends and what it's expected to unlock. Set a tight close timeline, two to four weeks is typical for a bridge, compared to the six to ten week timeline of a full priced round, since speed is the entire point of choosing this structure over a new equity round.

What Happens If You Can't Raise a Bridge Either?

If existing investors decline to bridge you and new investors aren't biting, it's a serious signal worth taking at face value rather than immediately shopping the same pitch to a wider list. Before assuming the company is out of options, revisit your own numbers first: rerun your financial model against a leaner plan, since a smaller, more targeted bridge tied to a shorter, more specific milestone is sometimes fundable even when a larger one isn't. Consider whether a revenue-based financing option, a venture debt facility (if you already have some revenue and a prior priced round), or a structured extension from a single existing investor at tighter terms could bridge a smaller gap than a full new round would. If none of those are viable, an honest, early conversation with your board about a reduced-scope plan, an acquihire path, or an orderly wind-down is a far better outcome for everyone, including your ability to raise again in the future, than running out of cash without warning anyone.

Frequently Asked Questions

How much runway should a bridge round buy you? Most bridges target 9 to 12 months of additional runway, enough to clearly hit the next milestone with a buffer, rather than the bare minimum needed to survive.

Is a bridge round a bad signal to future investors? Not inherently. A well-explained, milestone-based bridge with a clear narrative is common and normal. What raises concern is an unexplained bridge, an all-insider round with no outside validation, or a company on its second or third bridge without hitting the milestones the prior ones were meant to fund.

What discount rate is typical on a bridge SAFE? Typically 10% to 20% off the price of the next priced round, similar to or slightly tighter than a standard first-round SAFE discount.

Should existing investors get better terms on a bridge than new investors? Often yes, existing investors sometimes get a modestly better discount or cap in exchange for moving quickly and skipping a full diligence process, though this varies by company and negotiating dynamics.

How is a bridge round different from a down round? A bridge defers the pricing question via a SAFE or note until the next priced round. A down round is itself a new priced equity round at a lower valuation than the last one. A poorly priced bridge cap can function like a down round economically, even without being structured as one.

Size your bridge correctly using the runway and burn calculator and model the milestone it buys you in our financial model tool before you set a target amount or start the conversation.

Further Reading

• What Is a Startup Financial Model?
• The Rule of 40 Explained
• Churn Rate Calculation and Cohort Analysis
• Runway and Burn Calculator
• Financial Model Pro