A convertible note is a short-term loan a startup takes from an investor that converts into equity later, typically when the company raises its next priced funding round. The investor wires cash, receives a promissory note carrying interest and a maturity date, and holds a contractual right to swap that debt for shares instead of asking for the money back. Founders reach for the structure because it postpones the hardest question in early-stage fundraising — what is the company worth — until there is enough traction to answer it. Two negotiated terms, a valuation cap and a discount rate, decide how many shares the investor eventually receives.
How the Loan Part Works
Strip away the conversion clause and a convertible note is an ordinary loan. There is a principal amount, an interest rate, and a maturity date. Until conversion happens, the money sits on the company’s balance sheet as a liability.
Interest rates on startup notes usually land between 2% and 8%, and must at least meet the IRS’s applicable federal rate to avoid imputed interest problems. Most founders and investors treat the rate as a minor term because the real economics live elsewhere. Interest accrues over the life of the note and is added to principal at conversion, so the investor converts a slightly larger balance than the amount originally wired.
Maturity dates typically sit 18 to 24 months out. That window gives the startup a defined runway to hit milestones and close a priced round. If the round doesn’t happen by maturity, the investor can usually demand repayment in cash or convert into common stock at a pre-agreed valuation. Demanding cash from a startup that doesn’t have any is rarely productive, so maturity events tend to end in either an extension or a conversion on whatever terms the parties can negotiate.
The debt classification does give the noteholder one real advantage. If the company fails outright before conversion, note investors stand ahead of every equity holder in the liquidation line. They rank behind secured creditors but ahead of preferred stockholders and founders. It is a modest layer of downside protection, and it is the main thing a note offers that a pure equity instrument does not.
The Two Terms That Drive the Outcome
The valuation cap and the discount rate are the terms that matter. They work differently but exist for the same reason: rewarding the investor who took a risk before there was enough information to price the company properly.
Valuation Cap
The cap sets a ceiling on the price at which the note converts, no matter how high the company’s valuation climbs by the time a priced round closes. If a note carries a $6 million cap and the Series A prices the company at $20 million, the noteholder converts at the per-share price implied by the $6 million valuation, not the $20 million one. Lower cap relative to the priced round means more shares for the noteholder. Seed-stage caps commonly range from $4 million to $12 million, but the actual number depends on sector, market conditions, and founder leverage.
Discount Rate
The discount gives the noteholder a straight percentage off whatever price the new investors pay per share. A 20% discount on a $1.00 Series A price means the noteholder converts at $0.80 per share. Discounts typically run 15% to 25%. When a note carries both a cap and a discount, the investor converts at whichever produces the lower price and therefore more shares. The two are compared at conversion, and the better deal applies automatically.
Running the Math
A concrete example makes the mechanics visible. An investor puts in $100,000 on a note with a $5 million cap, a 20% discount, and 5% annual interest. Two years later the startup raises a Series A at a $15 million pre-money valuation with 10 million fully diluted shares outstanding just before closing.
- Accrued balance: $100,000 principal plus $10,000 in accrued interest, so $110,000 converts.
- Series A price per share: $15 million divided by 10 million shares equals $1.50.
- Cap price: $5 million divided by 10 million shares equals $0.50.
- Discount price: $1.50 times 0.80 equals $1.20.
- Conversion price: $0.50, because the cap wins.
- Shares received: $110,000 divided by $0.50 equals 220,000 shares.
A Series A investor putting the same $110,000 into the priced round at $1.50 per share would receive roughly 73,333 shares. The cap tripled the early investor’s share count. That is the payoff for being early.
MFN and Pro-Rata Rights
Some early noteholders negotiate a most favored nation clause. If the startup later issues additional notes with a lower cap or higher discount before the priced round closes, the MFN clause automatically upgrades the original investor’s terms to match. It protects the first money in from being undercut by later fundraising on more generous terms.
Pro-rata rights give a noteholder the option to invest more in future rounds to maintain their ownership percentage. Without them, every new round dilutes earlier investors. Pro-rata rights are not standard in convertible notes, but institutional investors and experienced angels increasingly negotiate for them, often limited to the next financing.
When and How the Note Converts
The note agreement defines a “qualified financing” as a future equity round that meets a minimum fundraising threshold. That threshold is negotiated, often starting at $500,000 to $1 million. When the startup closes a round at or above that number and issues preferred stock to new investors, the note converts automatically. The noteholder surrenders the debt instrument and receives shares of the same class of preferred stock the new investors are buying, subject to the same rights and restrictions. The liability leaves the balance sheet and becomes equity.
Automatic conversion is mandatory. Once a qualified financing closes, the noteholder cannot choose to keep the debt. This keeps the company from carrying old debt alongside new equity and gives the new lead investor a clean cap table.
Things get messier if the maturity date arrives without a qualified financing. The noteholder can typically demand cash repayment, though both sides know it probably isn’t coming. More often, the note converts into common stock (sometimes a lightweight “shadow preferred” series) at a pre-agreed valuation, frequently the cap itself. Or the parties agree to extend maturity. The maturity scenario is where drafting matters most, because ambiguous provisions create leverage disputes at the worst possible time.
Convertible Note vs. SAFE
The Simple Agreement for Future Equity, introduced by Y Combinator in 2013, was built to solve specific annoyances with convertible notes, and searchers frequently confuse the two. A SAFE is not debt. It carries no interest rate, no maturity date, and no repayment obligation. The investor buys the right to receive equity in a future priced round. Because there is no loan to repay, there is no maturity cliff and no interest accrual complicating the conversion math.
The tradeoff is protection. A convertible noteholder has creditor rights: seniority over equity in liquidation, a contractual claim to repayment, and the leverage that comes with holding debt. A SAFE holder has none of that. If the company shuts down before a priced round, a SAFE holder sits behind all debt. For small checks into very early companies the difference may not matter much. For larger checks, the debt structure of a note is a meaningful safety net.
Tax treatment also diverges. Notes are clearly debt: interest accrues, the company may deduct it, and the investor reports it as income. SAFEs lack the hallmarks of debt and are usually treated as either equity or a derivative contract for tax purposes. That ambiguity can create filing-time headaches, especially for founders who didn’t plan for it.
Tax Considerations Both Sides Should Know
Tax treatment is where convertible notes stop being simple.
Interest Deduction and Phantom Income
While the note is outstanding, accruing interest is generally deductible by the company as a business expense.1Office of the Law Revision Counsel. 26 USC 163 – Interest Most early-stage startups have no taxable income, so the deduction feeds a net operating loss carryforward. Section 163(j) caps business interest deductions at 30% of adjusted taxable income, but businesses with average annual gross receipts of $31 million or less are exempt, which covers essentially every startup issuing its first convertible note.2Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense
The investor’s side is less pleasant. Accrued interest must be reported as ordinary income each year even though no cash arrives until conversion or repayment. This is phantom income with no matching cash flow, and it is a real cost.
Conversion Is Not Automatically Tax-Free
Founders often assume that swapping the note for stock is a nonevent for taxes. It usually isn’t that clean. Section 351 of the Internal Revenue Code allows tax-free transfers of property to a corporation in exchange for stock, but Section 351(d)(2) says stock issued for “indebtedness of the transferee corporation which is not evidenced by a security” doesn’t count as issued for “property.”3Office of the Law Revision Counsel. 26 USC 351 – Transfer to Corporation Controlled by Transferor The IRS has successfully argued that debt with a term of two and a half years or less doesn’t qualify as a “security” for this purpose. Since most convertible notes mature in 18 to 24 months, they likely fall outside Section 351 protection.
That doesn’t mean every conversion is taxable. It might qualify under other provisions depending on the facts, for example if the noteholder is part of a larger group of transferors who together control the corporation after the exchange. But nobody should assume tax-free treatment. A tax advisor needs to look at each conversion on its actual terms.
The QSBS Clock
Investors in C corporations with gross assets under $50 million may qualify for Section 1202’s exclusion of gain on the sale of qualified small business stock. For stock issued after September 27, 2010, the exclusion is 100% of the gain, up to the greater of $10 million or ten times the investor’s adjusted basis.4Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock Recent legislation raised the per-issuer exclusion to $15 million (indexed for inflation) and introduced a phased schedule for stock issued after July 4, 2025, allowing a partial exclusion beginning at three years rather than requiring the full five-year hold.
Here is the detail investors often miss: the QSBS holding period doesn’t start when you write the check for the note. It starts when the note converts into stock. A note that sits unconverted for two years followed by a five-year hold means seven years of total commitment before the full exclusion is available. The stock must also be acquired at original issuance in a domestic C corporation (not an S corp or LLC), and the company must use at least 80% of its assets in an active trade or business.
Securities Law in Brief
A convertible note is a security under federal law. Issuing one triggers registration requirements unless an exemption applies. Almost every startup note offering relies on Regulation D, specifically Rule 506(b) or Rule 506(c), to skip full SEC registration.
Under Rule 506(b) the company cannot use general solicitation — no public advertising, no mass emails to strangers. It can sell to unlimited accredited investors and up to 35 non-accredited investors, though including the latter triggers disclosure obligations most startups prefer to avoid. Rule 506(c) allows open advertising, but every purchaser must be accredited, and the company must take reasonable steps to verify that status; self-certification is not enough.5eCFR. 17 CFR 230.506 – Exemption for Limited Offers and Sales Without Regard to Dollar Amount of Offering
An individual qualifies as accredited with net worth over $1 million excluding a primary residence, or annual income above $200,000 individually or $300,000 with a spouse or partner in each of the prior two years, with a reasonable expectation of the same in the current year. Holders of a Series 7, Series 65, or Series 82 license also qualify.6U.S. Securities and Exchange Commission. Accredited Investors
After the first investor is irrevocably committed, the company has 15 calendar days to file a Form D notice with the SEC. If the deadline lands on a weekend or holiday it rolls to the next business day.7U.S. Securities and Exchange Commission. Filing a Form D Notice Form D is a notice, not a registration, but missing the deadline can jeopardize the Regulation D exemption. Most states also require a notice filing when securities are sold to their residents, with fees ranging from nothing to over $2,000.
Where These Deals Go Wrong
The most common founder mistake is stacking too many notes with low caps before a priced round, then discovering at Series A that early investors own a far larger slice of the company than anyone expected. Each note converts on its own cap, and the dilution compounds. A founder who raises $500,000 across three notes at a $4 million cap and then prices a Series A at $20 million will hand over significantly more equity than the raise amount alone would suggest. A pro forma cap table run before each new note is the only way to see the dilution before it lands.
Investors, on the other side, tend to underestimate maturity risk. If the company can’t raise a qualified financing and can’t repay, the noteholder’s leverage is mostly theoretical. Suing a startup for repayment usually accelerates its collapse and destroys any remaining value. The practical outcome at maturity is almost always an extension or a negotiated conversion, not the cash repayment the note technically promises.
Both sides should watch for vague definitions. A note that doesn’t clearly define “qualified financing,” doesn’t specify whether the cap is pre-money or post-money, or fails to spell out the maturity scenario creates ambiguity that becomes expensive to resolve under pressure. Legal fees for a well-drafted note typically run $2,000 to $5,000, which is far less than the cost of fighting over an ambiguous one.