Convertible Notes Explained: How They Work, Key Terms, and When to Use Them

Complete guide to convertible notes for startup founders. How they work, key terms like interest, maturity, discount, and valuation cap, convertible note vs SAFE comparison, and a worked example with real numbers.

Before Y Combinator introduced the SAFE in 2013, the convertible note was the default instrument for early-stage startup fundraising. And despite the rise of SAFEs in Silicon Valley, convertible notes remain widely used — especially outside the Valley, in international markets, and among angel investors who prefer the protections that come with a debt instrument.

If you are raising a pre-seed or seed round, there is a good chance someone will hand you a convertible note term sheet. Understanding exactly how it works — the interest, the maturity date, the cap, the discount, and how conversion math actually plays out — is not optional. It is your job as a founder to know this cold.

This guide walks through everything you need to know about convertible notes: how they work mechanically, the key terms you will negotiate, a worked example with real numbers, and an honest comparison of convertible notes versus SAFEs.

Disclaimer: This post is educational, not legal or financial advice. Work with a qualified startup attorney before signing any financing documents.

What Is a Convertible Note?

A convertible note is a short-term loan that converts into equity in your company at a future date — typically when you raise a priced equity round (like a Series Seed or Series A).

Here is the basic idea: an investor lends you money today. Instead of paying back that loan with cash plus interest (like a traditional loan), the investor gets paid back in shares of your company when you raise your next round. Because the investor took the risk of investing early, they get to convert at a better price than the new investors in that round.

That "better price" comes from two mechanisms: a valuation cap and a discount rate. We will cover both in detail below.

From a legal standpoint, a convertible note is a debt instrument. Your company owes the investor money. It sits on your balance sheet as a liability until it converts. This matters for a few reasons that we will get into, but the most important one is this: if the note reaches its maturity date and you have not raised a qualifying round, the investor technically has the right to ask for their money back.

How Convertible Notes Work: Step by Step

The lifecycle of a convertible note follows a predictable pattern:

Step 1: The investment. An investor writes you a check — say $200,000. You sign a convertible note agreement that specifies the interest rate, maturity date, valuation cap, discount rate, and what constitutes a qualified financing event.

Step 2: Interest accrues. Unlike a SAFE, a convertible note is a loan, and loans accrue interest. The interest rate is typically modest (2-8% annually), and the interest does not get paid out in cash. Instead, it adds to the principal amount that will eventually convert into equity.

Step 3: A triggering event occurs. The most common trigger is a qualified financing — meaning you raise an equity round above a certain dollar threshold (often $1M or more). When that happens, the note converts automatically.

Step 4: Conversion. The total amount owed — the original principal plus all accrued interest — converts into shares of your company. The conversion price is determined by whichever gives the investor the better deal: the valuation cap or the discount rate applied to the new round's price per share.

Step 5: The investor holds equity. After conversion, the note is extinguished. The investor now owns preferred shares (or sometimes common shares, depending on the terms) just like the investors in the new round, except they paid a lower effective price per share.

Key Convertible Note Terms

Every convertible note has a handful of core terms that you need to understand and negotiate thoughtfully.

1. Principal

The principal is simply the investment amount — the money the investor is lending you. If an investor puts in $200,000, the principal is $200,000. This is the base amount that accrues interest and eventually converts.

2. Interest Rate

Because a convertible note is technically debt, it carries an interest rate. Typical rates range from 2% to 8% annually, with 5% being a common middle ground.

The interest is almost never paid in cash. Instead, it accrues and gets added to the principal at conversion. So if you have a $200,000 note at 5% annual interest and it converts after 18 months, the total converting amount is $215,000 ($200,000 principal + $15,000 in accrued interest).

Some founders see the interest as a minor nuisance. It is — in dollar terms, we are not talking about huge amounts. But it does mean more dilution at conversion, and it adds up if you have multiple notes outstanding or if it takes longer than expected to raise your next round.

3. Maturity Date

The maturity date is the deadline by which the note must either convert or be repaid. Most convertible notes have a maturity period of 12 to 24 months, with 18 months being common.

This is one of the biggest differences between a convertible note and a SAFE. A SAFE has no maturity date — it sits there quietly until a triggering event occurs, even if that takes years. A convertible note has a clock ticking.

What happens at maturity is one of the most important things to understand, and I cover it in detail below.

4. Valuation Cap

The valuation cap sets a maximum company valuation at which the note will convert. It protects the early investor from excessive dilution if your company's valuation increases dramatically between the note and the next round.

Here is how it works: if your note has a $5M cap and you raise your Series Seed at a $15M pre-money valuation, the note does not convert at $15M. It converts as if the valuation were $5M — giving the note holder significantly more shares per dollar invested.

The valuation cap is typically the most heavily negotiated term. Founders want a higher cap (less dilution); investors want a lower cap (more upside). The right number depends on your traction, market, and how much leverage you have.

5. Discount Rate

The discount rate gives the note holder a percentage reduction on the price per share paid by the new round's investors. Typical discounts range from 15% to 25%, with 20% being the most common.

If the Series Seed investors pay $1.00 per share and the note has a 20% discount, the note converts at $0.80 per share.

Most convertible notes have both a valuation cap and a discount rate. At conversion, the investor gets whichever produces the lower price per share (meaning more shares for the investor). They do not stack — the investor gets the better of the two, not both applied together.

6. Qualified Financing Threshold

The qualified financing threshold is the minimum amount your next equity round must raise to trigger automatic conversion. This is typically set at $1M to $2M, though it varies.

If you raise a small round that falls below this threshold, the note does not automatically convert. You and the investor would need to negotiate what happens — often the note holders can choose to convert voluntarily, or the note simply continues accruing interest until a qualifying round occurs.

7. Conversion Mechanics

The conversion mechanics spell out exactly how the note converts — what class of shares the investor receives, whether they get the same rights as the new round investors, and how the price per share is calculated.

In most standard convertible notes, the investor receives the same class of preferred stock as the new round investors, but at the lower conversion price. Some notes convert into common stock instead, which is less favorable for the investor and less standard.

Convertible Note Math: A Worked Example

Let me walk through a concrete example so the math is crystal clear.

The setup:

Investment amount (principal): $200,000
Interest rate: 5% per year (simple interest)
Valuation cap: $5,000,000
Discount rate: 20%
The note converts 18 months later at a Series Seed round

The Series Seed terms:

Pre-money valuation: $8,000,000
Price per share: $2.00
Total shares outstanding (pre-round): 4,000,000

Step 1: Calculate accrued interest.

$200,000 x 5% x 1.5 years = $15,000

Total converting amount: $200,000 + $15,000 = $215,000

Step 2: Calculate the conversion price using the valuation cap.

Cap price = Valuation cap / Pre-money shares outstanding

Cap price = $5,000,000 / 4,000,000 = $1.25 per share

Step 3: Calculate the conversion price using the discount.

Discount price = Series Seed price x (1 - discount rate)

Discount price = $2.00 x (1 - 0.20) = $2.00 x 0.80 = $1.60 per share

Step 4: Use the lower price.

The cap gives a price of $1.25 per share. The discount gives $1.60 per share. The investor gets the lower price: $1.25 per share.

Step 5: Calculate shares issued.

Shares = Total converting amount / Conversion price

Shares = $215,000 / $1.25 = 172,000 shares

For comparison, if the investor had simply invested $215,000 in the Series Seed at the $2.00 price, they would have received 107,500 shares. The convertible note gave them 172,000 shares — roughly 60% more — as compensation for investing early and taking more risk.

Convertible Note vs SAFE: Which Should You Use?

The SAFE (Simple Agreement for Future Equity) was created by Y Combinator as a simpler alternative to convertible notes. Both accomplish the same fundamental goal — letting you raise money before setting a valuation — but they differ in important ways.

Feature	Convertible Note	SAFE
Legal structure	Debt (loan)	Equity-like (not debt, not equity)
Interest	Yes (2-8% annually)	No
Maturity date	Yes (12-24 months)	No
Legal complexity	Moderate — more terms to negotiate	Simple — standardized documents
Legal cost	$2,000-$5,000+ per note	Often under $1,000 using templates
Investor protections	Stronger (debt = legal claim)	Weaker (no repayment right)
Common in Silicon Valley	Less common for first rounds	Standard for pre-seed/seed
Common outside SV	Very common	Gaining adoption but still less familiar
Balance sheet treatment	Liability (debt)	Varies by accounting treatment

For a deeper dive into SAFEs, including their own worked examples and terms, see our guide on SAFE notes explained.

When to choose a SAFE:

You are raising a pre-seed or seed round and want maximum simplicity
Your investors are familiar with and comfortable with SAFEs
You want to avoid interest accrual and maturity date pressure
You are in Silicon Valley or another market where SAFEs are standard

When to choose a convertible note:

Your investors specifically prefer or require a debt instrument
You are raising internationally where SAFEs may not be recognized
You are doing a bridge round between priced rounds
You want the discipline of a maturity date as a forcing function
Your attorney or investors are not familiar with SAFEs

In practice, the instrument often comes down to investor preference. If a strong angel writes you a check and they want a convertible note, you are probably not going to lose the deal over the instrument type. Understand the terms, negotiate what matters, and move on.

When to Use a Convertible Note

There are four common scenarios where a convertible note is the right choice:

1. Your investors prefer debt instruments. Many experienced angel investors and family offices prefer convertible notes because the debt structure gives them a legal claim on the company's assets. If things go sideways, a creditor has more legal standing than a SAFE holder. If your lead investor wants a note, there is usually no compelling reason to fight it.

2. International fundraising. SAFEs are an American invention, and they are not universally understood or legally recognized in every jurisdiction. If you are raising from investors in Europe, Asia, or other international markets, a convertible note is often the more familiar and legally straightforward instrument. Local counsel will know how to handle it.

3. Bridge rounds between priced rounds. If you have already raised a priced Series Seed and need capital to bridge to your Series A, a convertible note is the standard instrument. It acknowledges that a valuation was set in the prior round, adds modest interest as compensation for the bridge risk, and converts cleanly into the next round.

4. You want a maturity deadline. This one is counterintuitive, but some founders actually prefer having a maturity date. It creates urgency and a natural forcing function to either raise the next round or reach profitability. Without a deadline, it can be easy to drift. A convertible note with an 18-month maturity gives you a clear timeline.

What Happens at Maturity If You Have Not Raised?

This is the question that causes the most anxiety for founders holding convertible notes. The maturity date is approaching, you have not raised a qualifying round, and you owe your investors money.

In practice, there are three outcomes:

1. Extension (most common). The founder and investor agree to extend the maturity date — usually by 6 to 12 months. This is the most common outcome by far. Most angel investors are not in the business of demanding repayment from cash-strapped startups. They invested because they believe in you and the company, and they would rather give you more runway than trigger a crisis. That said, the investor may negotiate new terms for the extension — a lower cap, higher interest rate, or additional warrants.

2. Conversion at a negotiated valuation. The founder and investor agree to convert the note into equity at a mutually agreed-upon valuation, even without a qualifying round. This effectively turns the conversion into a small priced round between just the existing note holders and the company. The valuation is typically lower than the cap, reflecting the fact that you have not yet attracted new institutional investors.

3. Repayment (rare but possible). The investor demands repayment of the principal plus accrued interest. This is the nuclear option and it almost never happens in practice — repaying a $200K note would likely kill most early-stage startups, and the investor would end up with less than they would get from an equity conversion. However, the legal right exists, which is why some founders prefer SAFEs.

The key takeaway: communicate early and often with your note holders. If you see that you might not raise before maturity, start that conversation months in advance. Investors who are kept informed and feel respected are far more likely to extend.

Common Convertible Note Mistakes

Having seen plenty of fundraising rounds from both sides of the table, here are five mistakes founders make with convertible notes:

1. Not understanding the cap table impact. Founders often treat convertible notes as "free money" because conversion happens later. But every note you sign is future dilution. If you stack multiple notes with low caps, you can walk into your Series Seed already heavily diluted before the new investors even write their terms. Model your cap table with all outstanding notes converting before you sign the next one.

2. Ignoring the maturity date. Eighteen months sounds like a long time when you sign the note. It is not. If you are not on a clear path to raising your next round within 12 months, you need to start planning for what happens at maturity. Do not wait until the last month to start that conversation.

3. Negotiating the wrong terms. Some founders obsess over the interest rate (a minor cost) while ignoring the valuation cap (which drives the actual dilution). A 2% versus 6% interest rate on a $200K note over 18 months is a difference of $6,000. The cap, on the other hand, can mean a difference of hundreds of thousands of dollars in effective valuation. Focus your negotiation energy on the cap.

4. Raising too many notes over too long a period. If you do three separate convertible note rounds over two years — each with different caps, discounts, and interest rates — your cap table becomes a nightmare. Your attorney's bill for sorting out the conversion math alone will be painful. Keep your convertible note rounds tight and well-organized.

5. Not getting proper legal counsel. Convertible notes may be simpler than a full priced round, but they are still legal documents with real consequences. Using a template you found online without having a startup attorney review it is a false economy. Spend the money on proper legal work. It is usually a few thousand dollars and it protects you from terms you might not fully understand.

Conclusion

Convertible notes are a proven, well-understood instrument for early-stage fundraising. They are not as trendy as SAFEs in certain circles, but they remain the right tool in many situations — particularly for bridge rounds, international raises, and investors who prefer the protections of a debt instrument.

The keys to getting a convertible note right are straightforward: understand every term before you sign, model the conversion math so you know exactly how much dilution you are taking, communicate proactively with your note holders, and get proper legal counsel.

If you are preparing for a priced round, the Series A funding guide covers what you need to know about institutional fundraising. And for a comparison with the other common early-stage instrument, see our guide on SAFE notes explained.