How Convertible Note Interest and Maturity Work

Convertible notes are debt instruments that accrue interest over their term and convert into equity upon a triggering event—typically a qualified financing round. Interest rates generally range from 5–8% simple interest per year, and the accrued interest converts alongside the principal into shares at a discount. If the note reaches its maturity date (usually 18–24 months) without a conversion event, founders face a negotiation with noteholders about extension, conversion, or repayment.

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How Interest Accrues on Convertible Notes

A convertible note is, at its core, a loan. And like any loan, it carries an interest rate. But unlike traditional debt where interest is paid periodically in cash, convertible note interest accrues and is added to the principal amount that eventually converts into equity. No cash changes hands for interest payments during the life of the note.

Typical Interest Rates

Market rates for convertible notes in startup financings generally fall between 5% and 8% annually. The specific rate depends on several factors:

• Stage of the company. Pre-revenue companies typically see rates at the higher end (6–8%), while companies with meaningful traction may negotiate lower rates.
• Market conditions. In frothy markets, founders have more leverage and rates compress toward the lower end. In tighter markets, investors push rates higher.
• Note term. Longer maturity periods sometimes correlate with slightly higher rates to compensate investors for the extended timeline.
• Relationship dynamics. Angel investors writing smaller checks may accept lower rates than institutional investors with more standardized terms.

The interest rate on a convertible note isn't really about generating a return on the debt—it's a regulatory and structural requirement. The IRS requires debt instruments to carry a minimum interest rate (the Applicable Federal Rate, or AFR) to avoid imputed interest issues. Most convertible note rates exceed the AFR, but the principle matters: the interest rate exists partly for tax compliance, not just economic negotiation.

Simple vs. Compound Interest

The vast majority of startup convertible notes use simple interest, not compound interest. This is an important distinction:

• Simple interest: Calculated only on the original principal. A $100,000 note at 6% simple interest accrues $6,000 per year, regardless of how long the note has been outstanding.
• Compound interest: Calculated on the principal plus previously accrued interest. That same $100,000 note at 6% compounded annually would accrue $6,000 in year one, $6,360 in year two, and so on.

For the relatively short terms of most convertible notes (12–24 months), the difference between simple and compound interest is modest. On a $500,000 note at 6% over 18 months:

• Simple interest: $45,000
• Compound interest (annual): $46,362

The $1,362 difference rarely moves the needle in a venture financing context. But it's worth confirming in the note terms. If the note simply says "interest at 6% per annum" without specifying, courts in most jurisdictions will default to simple interest—but why leave it ambiguous?

How Accrued Interest Affects Conversion

When the note converts—whether at a qualified financing, maturity, or change of control—the accrued interest is added to the principal to determine the total conversion amount. If a $500,000 note has accrued $37,500 in interest at the time of conversion, the noteholder converts $537,500 worth of equity.

This conversion happens at the same terms as the principal: subject to any valuation cap or discount rate in the note. So the interest doesn't just give the investor more shares—it gives them more discounted shares. On a note with a 20% discount, that $37,500 in interest effectively buys equity at 80 cents on the dollar compared to the new investors in the priced round.

For a deeper comparison of convertible notes versus SAFEs (which don't carry interest), see our guide on SAFEs vs. convertible notes.

What Happens at Maturity

The maturity date is when the note comes due. If no conversion event has occurred by that date, the company technically owes the noteholders their principal plus accrued interest in cash. This is where things get interesting—and sometimes contentious.

The Maturity Default Dynamic

In practice, almost no one expects a startup to repay a convertible note in cash at maturity. The investors wrote convertible notes because they wanted equity exposure, not a fixed-income return. And the startup almost certainly doesn't have the cash to repay the notes—that's the whole reason it was raising convertible debt in the first place.

But the legal right to demand repayment creates leverage. When a note matures without conversion, the noteholders have several options:

1. Demand repayment. Legally available but practically rare. Forcing repayment could push the company into insolvency, destroying the investors' own position. But the threat of repayment is a powerful negotiating tool.

2. Negotiate conversion. The most common outcome. Noteholders and the company agree on conversion terms—typically a negotiated valuation that reflects the company's current stage. This is essentially a mini-priced round driven by the maturity event.

3. Extend the maturity date. The simplest solution when both sides want more time. The note is amended to push out the maturity date, sometimes with sweetened terms (a lower cap, higher discount, or additional warrant coverage) to compensate investors for the extended timeline.

4. Convert at the cap. Many well-drafted notes include an automatic or optional conversion at the valuation cap upon maturity, eliminating the need for negotiation. This is increasingly standard and is the cleanest outcome for both sides.

Maturity Date Length: Finding the Right Balance

Standard maturity periods range from 12 to 24 months, with 18 months being the most common. The right term depends on the company's fundraising timeline:

• Too short (< 12 months): Creates unnecessary pressure on founders to raise a priced round quickly. If the round takes longer than expected (which it often does), you're negotiating an extension before you've had time to execute.
• Too long (> 24 months): Reduces investors' leverage and may signal to the market that the company doesn't expect to raise a priced round soon. Also creates more accrued interest, increasing dilution at conversion.
• The sweet spot (18 months): Gives founders enough runway to hit milestones and raise a Series A or Series Seed while keeping a reasonable timeline for conversion.

Some notes include an automatic extension provision—if the company has raised at least X dollars in revenue or reached certain milestones, the maturity date automatically extends by 6–12 months. This is a founder-friendly provision worth negotiating.

Qualified Financing Triggers

The primary conversion mechanism for a convertible note is the qualified financing—a priced equity round that meets certain thresholds defined in the note.

Defining "Qualified Financing"

The qualified financing threshold is the minimum amount raised in the subsequent equity round that triggers automatic conversion of the notes. Typical thresholds range from $500,000 to $3,000,000, depending on the size of the note round and the anticipated next round.

Key considerations when setting this threshold:

• Set it high enough to ensure conversion only happens in a meaningful round that establishes a real valuation. You don't want the notes converting on a $200,000 bridge round at terms that weren't negotiated for that purpose.
• Set it low enough that you're not trapped. If the threshold is $2 million and you can only raise $1.5 million, you'll need noteholder consent to convert—giving them leverage over terms.
• Exclude the notes themselves. The qualified financing amount should not count the converting notes toward the threshold. A $1 million note round with a $1 million qualified financing threshold would otherwise convert into itself.

Conversion Mechanics

Upon a qualified financing, the notes convert automatically. The conversion price is the lower of:

1. The price per share paid by new investors in the qualified financing, multiplied by (1 minus the discount rate), or
2. The price per share implied by dividing the valuation cap by the company's fully-diluted capitalization.

This "lower of" structure ensures noteholders get the more favorable conversion price. In a rapidly appreciating company, the cap typically controls. In a company that raises at or below the cap, the discount controls.

For a detailed explanation of how caps and discounts interact with dilution, see our article on how startup equity dilution works.

What Shares Do Noteholders Receive?

In most qualified financings, converting noteholders receive the same class of preferred stock issued to the new investors—but potentially at a lower price per share (due to the cap or discount). Some notes specify that noteholders receive a separate series of preferred stock (e.g., "Series Seed-1" instead of "Series Seed") with identical terms but a different conversion price. This is a cleaner approach from a cap table management perspective.

The type of preferred stock received matters for liquidation preferences. If noteholders receive the same series as new investors, they share the same liquidation preference stack. If they receive a separate series, their preference is calculated independently—which can create complications in a downside scenario.

Practical Negotiation Points

Interest Rate

Don't over-negotiate the interest rate. The difference between 5% and 8% on a $500,000 note over 18 months is $11,250—trivial in the context of a venture financing. Spend your negotiating capital on the cap, discount, and structural terms that actually drive economics.

That said, if an investor pushes for an unusually high rate (10%+), push back. High interest rates can signal that the investor views this as debt rather than a bridge to equity, which misaligns incentives.

Maturity Conversion Terms

Negotiate the maturity conversion terms upfront. The note should specify what happens if it reaches maturity without a qualified financing:

• Best for founders: Automatic conversion at the cap valuation, or at the company's option.
• Best for investors: Note becomes immediately due and payable, or converts at a discounted valuation set by mutual agreement.
• Compromise: Conversion at the cap with a majority-in-interest noteholder consent, or automatic extension for 6–12 months.

Most Favored Nation (MFN) Clauses

Some convertible notes include an MFN clause providing that if the company issues subsequent convertible instruments on more favorable terms, the existing noteholders can adopt those terms. This is particularly relevant when companies do multiple convertible note rounds—if the second round has a lower cap, MFN noteholders from the first round can match it.

MFN clauses are standard in SAFEs (the post-money SAFE includes one by default) and increasingly common in convertible notes. They're generally founder-friendly to accept because they only trigger if you actually offer better terms to later investors.

Amendment and Waiver Provisions

The note should specify what percentage of noteholders (by principal amount) can amend the note terms or waive provisions. Typical thresholds are a simple majority (>50%) or a supermajority (≥66.7%) by outstanding principal.

This matters more than founders realize. If you have 15 noteholders and need unanimous consent to extend the maturity date, one holdout can create a crisis. Majority-in-interest amendment provisions give you flexibility to manage the cap table without herding cats.

Tax Implications

Original Issue Discount (OID)

If a convertible note is issued at a discount to its stated redemption price (which can happen if the conversion features create OID under the tax code), both the company and the investor may have tax reporting obligations. In practice, most startup convertible notes are structured to minimize OID issues, but it's worth flagging with your tax advisor.

Interest Income

Even though no cash interest payments are made, investors technically accrue taxable interest income on the note. For cash-basis individual investors, this generally isn't recognized until the note converts or is repaid. But for accrual-basis investors (including some funds), interest income is recognized as it accrues. This is a tax issue for the investor, not the company, but founders should be aware of it when investors raise concerns.

QSBS Implications

One underappreciated issue: time spent as a noteholder generally does not count toward the five-year holding period required for QSBS (Section 1202) benefits. The holding period starts when the note converts into qualified small business stock, not when the note was issued. For notes that remain outstanding for 18+ months, this can meaningfully delay the investor's path to QSBS eligibility.

The Convertible Note in Context

Convertible notes remain a widely used instrument for seed-stage fundraising, despite the growing popularity of SAFEs. Their debt structure creates both advantages (interest accrual, maturity date leverage for investors, established legal framework) and disadvantages (maturity default risk, potential balance sheet issues, more complex documentation).

For founders evaluating their options, the interest and maturity mechanics described above are the key structural differences between notes and SAFEs. Understanding these mechanics—and negotiating them thoughtfully—can save significant dilution and avoid unnecessary founder-investor friction when the note reaches its conversion event.

For a broader view of how convertible instruments fit into the fundraising journey, see our guide on navigating seed to Series B equity financing.