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Series A vs Series B funding: what's the difference?
Series A vs Series B in one page: median round size, valuation and dilution, the metrics each round is judged on, who invests, and how long the gap between them runs.
Short answer: a Series A proves a startup can grow repeatably; a Series B pays to grow it much faster. A Series B is usually larger, sold at a much higher valuation and with less dilution, and investors judge it on revenue scale and efficiency rather than early signals.
Series A vs Series B at a glance
| Series A | Series B | |
|---|---|---|
| Purpose | Turn early traction into a repeatable model | Scale a proven model: more markets, products, people |
| Median round size | $14.4M | $25M |
| Median valuation | $80M | $191M |
| Median dilution | 18% | 12% |
| Typical lead | Early-stage VC firm | Growth-oriented VC firm, often a new lead |
| What investors check | Growth, retention, early unit economics | Revenue scale, efficiency, predictable sales |
| Board | Lead VC usually joins | Often adds a second investor seat |
Medians are for software startups on Carta in the first half of 2026. They vary widely by sector, and AI companies raise well above them.
What changes between the two rounds
- The questions get harder. At Series A investors ask "does this grow?". At Series B they ask "how efficiently, and how far?": sales efficiency, payback period, gross margin and net revenue retention.
- The money goes into scale. Series B pays for sales teams, new markets, new products and senior hires, not product discovery.
- The cap table matures. Series B usually brings a new lead investor, more board structure and sometimes secondary sales for early employees or angels.
What investors expect before a Series B
- A repeatable sales engine with predictable pipeline and conversion.
- Revenue at scale. For SaaS, often several times the revenue the company had at Series A, still growing fast.
- Efficiency. A sensible ratio of new revenue to sales and marketing spend.
- Leadership. A team that can run departments, not just ship product.
Series A to Series B: timing
- Expect a long gap. Companies that raised a Series B on Carta in Q1 2025 had waited a median of 2.8 years since their Series A, the longest interval on record.
- Plan Series A runway for that, and raise with 6 to 9 months of runway left.
- Not ready? An inside-led extension, a bridge round or venture debt can buy time to hit Series B metrics.
Related guides
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Questions
What is Series B funding?
Series B is the round after Series A, raised once a startup has a repeatable business model and needs capital to scale it: bigger sales teams, new markets and new products.
What is the difference between Series A and Series B?
Series A funds turning early traction into a repeatable model. Series B funds scaling that model. Series B rounds are larger, priced at higher valuations, cause less dilution and are judged on revenue scale and efficiency.
How much is a typical Series B round?
The median Series B for software startups on Carta in the first half of 2026 was $25M at a $191M valuation, against a median Series A of $14.4M at an $80M valuation.
How much dilution is typical at Series B?
Median Series B dilution was about 12% in 2026, lower than the roughly 18% typical at seed and Series A.
How long is the gap between Series A and Series B?
It has been getting longer. Companies that raised a Series B on Carta in Q1 2025 had waited a median of 2.8 years since their Series A.
Who invests in Series B rounds?
Larger venture capital firms and growth-stage investors usually lead, often a new investor rather than the Series A lead, with existing investors taking their pro rata.
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