Convertible Note Calculator

Both instruments convert to equity at a priced round, but they differ structurally. A convertible note is debt: it carries an interest rate (typically 4-8%), has a maturity date (usually 12-24 months), and creates a legal obligation to repay if not converted. A SAFE is not debt: it has no interest, no maturity date, and cannot be called. The SAFE was designed by Y Combinator in 2013 to eliminate the complexity and administrative burden of convertible notes. Convertible notes offer investors additional protections (maturity forcing function, repayment right, interest accrual) while SAFEs are simpler and more founder-friendly. In practice, the most significant differences at conversion are that convertible notes carry accrued interest (increasing the conversion amount by 10-20% for typical holding periods) and that maturity dates create leverage for investors.

In most startup convertible notes, interest is not paid in cash during the life of the note. Instead, it accrues and is added to the principal at conversion — the noteholder receives equity representing both the principal and the accrued interest. This is called payment-in-kind (PIK) interest. Some notes specify compound interest (interest accrues on the growing principal+interest balance) while others specify simple interest (interest accrues only on the original principal). The difference matters: $500,000 at 8% compounded monthly for 18 months accrues $63,077, while the same note with simple interest accrues exactly $60,000. Always check whether interest is simple or compound when analyzing convertible notes.

When a convertible note reaches its maturity date without a qualifying financing event, the company technically defaults on its debt obligation. In practice, this almost never results in forced repayment because startups rarely have the cash, and sophisticated investors know that forcing repayment might kill the company they are trying to invest in. Instead, founders and investors typically negotiate: (1) an extension agreement granting 12-18 more months, often with improved investor terms such as a lower valuation cap, higher interest rate, or warrant coverage; (2) automatic conversion into equity at a predetermined price (some notes include this provision); (3) conversion at a negotiated price that is below what a priced round would establish. The maturity date gives investors leverage but is rarely used as a hard enforcement mechanism.

Warrant coverage is an additional incentive sometimes included in convertible note terms. Warrants give the investor the right (but not obligation) to purchase additional shares at a specified price (typically the conversion price) for a specified period. Common warrant coverage is 10-25% of the principal amount — an investor putting in $500,000 with 20% warrant coverage receives warrants to purchase shares worth an additional $100,000 at the conversion price. Warrants are sometimes added to make convertible notes more attractive in difficult fundraising environments, to compensate for maturity date extensions, or to attract larger checks. Warrants add modest additional dilution but can be significant for large notes.

Convertible notes appear on the balance sheet as liabilities (debt) until they convert. They do not appear on the equity cap table until conversion. However, investors and founders track the shadow cap table — a pro-forma view of what the cap table will look like after conversion, usually modeled at the expected Series A terms. This shadow cap table is essential for accurate dilution modeling, as the converting notes will create significant new shares. When building a pro-forma for a Series A, the investor's model will include note conversions in the fully diluted pre-money share count, affecting the per-share price and dilution calculations.

For most US early-stage startups, the post-money YC SAFE is simpler, cheaper (no legal fees for interest, maturity, and default provisions), and more founder-friendly. The SAFE is preferred when the investor community is comfortable with it (most US seed investors are), when the company wants to minimize legal complexity, and when the founder does not want a maturity date creating leverage for investors. Convertible notes may be preferable when investors specifically request debt treatment, when the financing is very small and the investor wants the maturity forcing function, in international markets where SAFE legal and tax treatment is uncertain, or when the company wants the ability to offer warrant coverage as an added incentive.

Without a valuation cap, a convertible note converts at a discounted price relative to the next round's price: Conversion Price = Series A Price x (1 - Discount Rate). If the discount is 20% and the Series A is $2/share, the note converts at $1.60/share. Without a cap or discount, the note typically converts at the Series A price — providing no economic advantage to the early-stage investor relative to a Series A investor, which fails to adequately compensate for the significantly higher risk taken at the early stage. Notes without caps or discounts are rare and generally considered below-market terms for investors.