A convertible note is a short-term loan to a startup that automatically converts into equity when a later funding round closes, letting the company raise money without agreeing on a valuation at the time of the investment. Understanding how convertible notes work comes down to four moving parts: the loan itself, the event that triggers conversion, the price adjustments (a valuation cap, a discount, or both) that reward the early investor, and what happens if the maturity date arrives before any of that plays out. Most notes carry interest rates between 2% and 8%, accrue that interest onto the balance rather than paying it in cash, and mature in 18 to 24 months.
The Loan Phase
Until something triggers conversion, a convertible note is a loan. The startup receives the principal, and the investor holds a promissory note that earns interest. That interest compounds onto the balance rather than arriving as periodic checks, so no cash changes hands during the life of the note. When conversion eventually happens, the accrued interest converts into shares alongside the principal, giving the investor a small bonus for the wait.
Nearly all startup convertible notes are unsecured. The investor has no priority claim on company assets if the business fails. If the startup also has a bank line of credit secured by its assets, that lender gets paid first in a liquidation, and note holders stand behind any secured creditors. This is standard for early-stage deals. Investors accept the risk because they’re betting on conversion into equity, not on repayment.
Some notes include a most-favored-nation clause. If the company later issues notes to new investors on better terms, the earlier investor can adopt those improved terms. It protects early backers from being penalized for investing before the company had leverage to negotiate.
What Triggers Conversion
The note stays as debt until a specific event in the contract forces it to convert. Most agreements list two or three.
- Qualified financing. The most common trigger. The startup closes a priced equity round, often a Series A, that raises at least a specified minimum, frequently $1 million or more. Once that threshold is met, the note balance converts into the same class of preferred stock issued to the new investors.
- Change of control. The company is acquired, merges, or sells a majority of its voting power. The note typically converts immediately before the transaction closes so the note holder participates in the acquisition proceeds as a shareholder rather than a creditor.
- Initial public offering. If the startup goes public, the note converts into shares just before listing. Rare at the note stage, but included as a catch-all.
Qualified financing does the heavy lifting in practice. The other triggers are safety nets designed to make sure the investor doesn’t end up holding debt through a major liquidity event. Some agreements also grant pro-rata rights, which let the note holder invest additional money in the triggering round to maintain their ownership percentage.
Valuation Caps as a Price Ceiling
A valuation cap sets the maximum company valuation at which the note can convert, no matter how high the actual valuation climbs before a trigger fires. It rewards early investors for taking a bet before the company proved itself.
The math is what matters. Say you invest $100,000 with a $5 million valuation cap. The startup later raises a Series A at a $10 million pre-money valuation, and new investors pay $1.00 per share. Without the cap, your $100,000 would buy 100,000 shares at that price. But the cap limits your conversion valuation to $5 million, half the actual valuation. Your effective share price becomes $0.50 ($5 million cap ÷ $10 million valuation × $1.00 per share), so your $100,000 buys 200,000 shares. You end up with twice the ownership of a new investor who put in the same amount at the Series A.
The wider the gap between the cap and the actual valuation, the bigger the payoff. If that same company raised at a $20 million valuation instead, your effective price would drop to $0.25 per share, turning $100,000 into 400,000 shares. The cap is a fixed number that never moves. It’s the single most negotiated term in a convertible note because it determines the ceiling on what you pay per share.
How Discount Rates Work
A discount rate gives the note holder a straight percentage reduction off whatever price new investors pay in the triggering round. A 20% discount is the most common figure. If new investors pay $1.00 per share, the note holder converts at $0.80. A $100,000 investment would buy 125,000 shares at the discounted price.
The discount rewards the early investor for taking risk, but its value scales differently from a cap. A discount is always a fixed percentage off the round price, regardless of how high the valuation goes. A cap becomes more valuable as the company’s valuation climbs. When both terms appear in the same note, the investor converts at whichever produces the lower price per share. In the examples above, the cap produced a $0.50 share price while the 20% discount produced $0.80, so the cap wins. If the Series A had come in at a $6 million valuation instead, the cap price would be roughly $0.83, making the $0.80 discount the better deal. The investor doesn’t choose in advance. The contract simply applies whichever calculation results in more shares.
What Happens if the Maturity Date Arrives First
If maturity arrives and no conversion trigger has occurred, the note doesn’t quietly expire. The investor holds a debt instrument that is legally due, and the contract governs what happens next.
Repayment or Default
The investor can demand full repayment of principal plus accrued interest. Most early-stage startups don’t have the cash, which creates a technical default. Some notes specify a higher default interest rate that kicks in after a missed payment. A note carrying 8% annual interest might jump to 10% or whatever maximum state law allows once a default event occurs.1SEC.gov. Convertible Note In practice, note holders at the seed stage rarely push a company into bankruptcy over a matured note because a dead company repays nothing.
Extension
The more common path is an amendment extending the maturity date by another 12 to 24 months. Both sides usually agree because the investor wants equity, not a lawsuit, and the founder wants to avoid default. Extensions sometimes come with improved terms for the investor, such as a lower valuation cap or a warrant to purchase additional shares.
Automatic Maturity Conversion
Some agreements convert the debt into equity automatically at maturity if no qualified financing has occurred. When this triggers, the note typically converts into common stock rather than preferred stock, and the conversion price is either pre-negotiated in the original agreement or based on a fair market value assessment at the time. Common stock carries fewer protections than the preferred stock an investor would have received through a qualified financing conversion, so this outcome is less favorable but still gives the investor an ownership stake.
Tax Consequences Investors Miss
The tax treatment of convertible notes catches many angel investors by surprise because obligations can arise before any cash changes hands.
Original Issue Discount
When a note accrues interest that gets added to the balance rather than paid out, the IRS may treat the accrued amount as original issue discount (OID). OID is the difference between what the investor paid for the note and what the note is ultimately worth at maturity or conversion, and federal law treats it as a form of interest income.2Internal Revenue Service. Topic No. 403, Interest Received Under Section 1272 of the Internal Revenue Code, the holder of a debt instrument with OID must include a portion of that discount in gross income each year, even if no cash payment is received.3Office of the Law Revision Counsel. 26 USC 1272 – Current Inclusion in Income of Original Issue Discount You could owe tax on interest you never actually received.
Conversion Itself
The conversion, where the debt balance transforms into shares, is generally not a taxable event. IRS Publication 550 states that converting bonds into stock of the same corporation according to a conversion privilege in the instrument’s terms typically does not produce a recognized gain or loss.4Internal Revenue Service. Publication 550, Investment Income and Expenses The accrued interest that converts into additional shares, however, is treated as constructive receipt of income. You owe tax on that interest in the year of conversion, even though it was paid in stock. Your tax basis in the new shares should be increased by the amount of interest income you recognized.
The QSBS Holding Period Trap
Section 1202 of the Internal Revenue Code allows investors to exclude up to 100% of the gain on qualified small business stock (QSBS) held for five years or more.5Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock The exclusion is significant enough that many angel investors build return models around it. Here’s the catch: a convertible note is not stock until it converts. The five-year holding period doesn’t begin when you write the check. It begins on the date the note converts into shares. Since conversion often takes 18 to 24 months after issuance, the effective holding period for QSBS purposes can stretch to seven years from the original investment. Missing this detail can mean the difference between a tax-free exit and a substantial capital gains bill.
A Note on SAFEs
A Simple Agreement for Future Equity (SAFE) is a different instrument that often gets grouped with convertible notes. A SAFE is legally an equity instrument, not debt. It carries no interest and no maturity date, so there’s no ticking clock and no accrued balance to convert. SAFEs typically convert at any priced equity round, without the minimum-raise threshold most notes require. Both instruments commonly include a cap, a discount, or both, and the conversion math works similarly once a trigger fires. If you’re evaluating a startup investment described as a “SAFE,” the maturity and interest sections above don’t apply.