The Convertible Note Overhang Problem: Why Uncapped Notes From Your Seed Round Are a Series B Red Flag

Founders rarely think about the convertible notes they signed at seed by the time they are preparing a Series B. The notes are sitting in a data room folder. The business has grown. The problem feels like ancient history.

It is not. When a Series B lead investor opens your cap table, those uncapped notes are one of the first things they model. As part of the broader cap table risk cluster, uncapped note overhang is a structural issue, not a legacy paperwork detail. It changes the ownership math before terms are proposed, and institutional investors treat unresolved dilution uncertainty as a signal about cap table discipline across the entire company.

What an Uncapped Convertible Note Actually Does at Series B

A convertible note is debt that converts into equity at a future priced round. Most seed-stage notes include two protective terms for investors: a valuation cap and a discount rate. The investor converts at whichever produces the lower price per share, giving them more equity for their money.

The cap sets a ceiling. It says: no matter how high the Series B valuation goes, the note converts as if the company were worth no more than X. That ceiling protects the noteholder's return and, critically, makes the dilution math predictable for founders and incoming investors.

An uncapped note removes that ceiling entirely.

The discount still applies to an uncapped note. But without a cap, the conversion price drops in proportion to the round price. A 20% discount at a $200M Series B valuation produces a very different share count than the same discount at a $60M Series A. The noteholder benefits more as the company's valuation grows. The founder absorbs that benefit in the form of dilution they cannot fully predict until the round price is set.

That is the core mechanics problem. The investor diligence problem is different, and it is more serious.

Why Institutional Lead Investors Treat Note Overhang as a Structural Problem

A Series B lead is not reviewing your cap table to understand the history. They are stress-testing the post-money ownership stack to see whether the deal works after everything converts, the option pool gets refreshed, and new money comes in.

Uncapped notes make that test harder. According to Carta's convertible note modeling guidance, a proper note conversion model requires the principal amount, assumed accrued interest, the discount rate, the priced round assumptions, and the option pool size - all at once. When any of those inputs is uncertain, the ownership output is uncertain. Uncapped notes add a layer of uncertainty that capped notes do not: the final share count cannot be confirmed until the round price is locked.

Here is what an institutional lead investor is actually working through when they see uncapped notes on your cap table:

• What is the total principal plus accrued interest across all outstanding notes?
• At our target Series B price, what share count does each note produce after the discount?
• After note conversion, option pool refresh, and new money, what does the founder ownership look like?
• Is founder ownership still sufficient to keep the team aligned and incentivized post-close?
• Does the note overhang leave enough room for the lead to take the target stake without forcing a structure that looks punitive?
• Are there multiple notes at different discount rates, maturity dates, or side-letter terms that compound the uncertainty?

None of these questions are unanswerable. But uncapped notes force the investor to model multiple scenarios before they can answer any of them. That extra modeling step signals cap table complexity. And in competitive deal environments, complexity that the investor has to resolve - rather than complexity the founder has already resolved - slows engagement or stops it.

The Math Problem Founders Miss: Discount Plus No Ceiling Equals Open-Ended Dilution

Here is a simplified example to make the open-ended dilution concrete.

A founder raised $1.5M in seed capital via an uncapped convertible note with a 20% discount and 6% annual interest. The note has been outstanding for two years. By the time the Series B closes, the total obligation including accrued interest is approximately $1.68M.

The Series B closes at a $150M pre-money valuation on 10 million fully diluted shares, giving a share price of $15.00. The note converts at a 20% discount, so the effective conversion price is $12.00 per share.

‍The key insight: the share count changes with every scenario. At a lower valuation, the note converts into more shares. At a higher valuation, it converts into fewer. There is no fixed ceiling telling the founder or the lead investor exactly what the noteholder will own until the round price is set.

That uncertainty is what IRC Partners' Cap Table Forensics process routinely surfaces: founders often own 5-15% less than expected once prior convertibles are fully modeled across realistic round scenarios. The gap is not always dramatic. But when a Series B lead is trying to confirm that founders still own enough to stay motivated after the round, even a 2-3% variance in noteholder ownership can change the deal structure conversation.

The real problem is not the discount itself. Most institutional investors expect some discount on seed-stage risk capital. The problem is that without a cap, the dilution outcome is tied to a future round price the founder does not control at the time the note is signed.

How Uncapped Note Overhang Spills Into the Rest of the Series B Cap Table

Uncapped note conversion rarely sits in isolation. It interacts with every other instrument on the cap table, and those interactions are what institutional investors are really stress-testing.

Four spillover effects that compound the problem:

1. SAFE stack interaction. If you also raised SAFEs alongside uncapped notes, both instruments convert at the same priced round. The combined dilution from multiple convertibles converting simultaneously is almost always larger than founders estimate. The article You Raised Three SAFEs. Here's How They're About to Detonate at Your Series B covers how stacked SAFEs compound this effect.
2. Option pool pressure. Series B investors typically require an option pool refresh before the round closes. That refresh is calculated on the post-money fully diluted share count - which now includes the converted note shares. More converted shares means a larger pool refresh, which means more dilution for founders before new money even comes in.
3. Lead investor stake compression. If the note and SAFE conversions produce more shares than expected, the lead investor may need to invest more to reach their target ownership percentage. That changes the round economics and can affect valuation negotiations.
4. Cap table signal. As How SAFE Notes and Convertible Notes Stack Up and Silently Destroy Your Series B Cap Table explains, institutional investors read uncapped instruments as a pattern. One uncapped note might be explained as a fast seed close. Multiple uncapped instruments across multiple rounds signals that the founder did not prioritize cap table structure during the early stages.

The investor's concern is not just the math. It is what the math says about how the company was built.

What Founders Should Do Before a Lead Investor Models the Round

The goal is simple: model the note conversion before the investor does. If you find a problem, fix it or disclose it with context. If the math works, present it cleanly so the investor does not have to build the model from scratch.

Pre-Series B note overhang checklist:

• Locate every outstanding convertible note and confirm the current principal balance
• Calculate accrued interest on each note based on the stated interest rate and time outstanding
• Confirm the discount rate and whether any side-letter modifications affect the conversion terms
• Confirm the maturity date and whether any extensions have been granted
• Run at least three conversion scenarios: your target Series B valuation, a 20% higher valuation, and a 20% lower valuation
• Layer in the option pool refresh requirement for each scenario to see total post-money dilution
• Confirm founder ownership is above the threshold your target investors typically require post-close
• If any scenario produces a cap table that no longer works, address it before outbound fundraising starts

The Capital Stack Explained guide on IRC Partners covers how stacked convertibles interact with later institutional rounds in more detail.

Founders who complete this prep keep the Series B conversation focused on the business. Founders who skip it hand the investor a modeling problem to solve before they can engage on terms. For a broader look at what else kills institutional raises before terms are discussed, the 10 mistakes that kill your first institutional raise is worth reading alongside this checklist.

Frequently Asked Questions‍

What is the difference between a capped and uncapped convertible note at Series B?

A capped convertible note converts at the lower of a fixed maximum valuation or the discounted round price. The cap creates a predictable ceiling on dilution. An uncapped note has no ceiling, so the conversion price is calculated purely as a percentage discount off the Series B share price. The higher the Series B valuation, the more favorable the discount becomes for the noteholder and the less predictable the dilution is for founders and incoming investors.

Do uncapped convertible notes automatically kill a Series B?

No. Uncapped notes are a diligence red flag because they introduce dilution uncertainty, not because they make a deal impossible. A founder who has modeled the conversion scenarios, confirmed that founder ownership remains viable post-close, and can present a clean fully diluted cap table will face far less friction than one who has not done that work. The issue is unresolved uncertainty, not the instrument itself.

When does accrued interest on a convertible note become a problem?

Accrued interest increases the total principal converting into equity. On a $1.5M note at 6% annual interest outstanding for three years, the conversion amount is approximately $1.77M rather than $1.5M. That 18% increase in conversion principal translates directly into additional shares issued to the noteholder. Founders who model only the original principal underestimate dilution by the full interest accrual, which can be material on larger notes or long-outstanding instruments.

Why do Series B investors care about seed-stage note terms they did not negotiate?

Because the seed-stage terms affect the post-money cap table they are buying into. A Series B lead investor is acquiring a stake in a company that already has legacy obligations. If those obligations convert in a way that compresses founder ownership below alignment thresholds or reduces the room available for the lead's target stake, the investor either reprices the deal or walks away. The origin of the note is irrelevant. The impact on the cap table at close is what matters.

Can a founder renegotiate or cap an uncapped convertible note before a Series B?

Yes, in principle. Noteholders can agree to add a valuation cap or modify conversion terms before a priced round. In practice, noteholders who hold uncapped notes benefit from the open-ended discount as valuations rise, so they have limited incentive to accept a cap unless offered something in return. Founders considering renegotiation should do so early, before the Series B process starts, and with counsel. Attempting to modify note terms mid-process creates additional diligence complexity.

What founder ownership percentage do Series B investors typically want to see post-close?

Most institutional Series B leads expect combined founder ownership of at least 20-30% post-money on a fully diluted basis, though thresholds vary by fund and deal structure. Below 15-20%, investors begin to question whether founders are sufficiently incentivized to drive the growth the round is designed to fund. Uncapped note conversion that pushes founders below that threshold, especially when combined with option pool refreshes, is one of the scenarios that causes a lead to restructure or reduce the round size.

How far in advance should founders audit uncapped notes before starting a Series B process?

At least six months before beginning outbound fundraising. That timeline gives founders room to model conversion scenarios, identify any cap table issues, engage noteholders about modifications if needed, and update the cap table software so the fully diluted view is accurate before the first investor data room is opened. Founders who start this process after receiving investor interest are already behind.

Continue reading this series:

• That Seed Round Term Looked Fine. It's Now Costing You $8M at Series B
• You Raised Three SAFEs. Here's How They're About to Detonate at Your Series B
• What Cap Table Issues Will Kill a Series B Before the Lead Investor Even Reads Your Deck

Most founders don't lose the raise because of the pitch. They lose it because the structure was wrong before the first investor call.IRC Partners advises founders raising $5M to $250M of institutional capital. 7 strategic partners per quarter. Start here to schedule a call with our team.