If you've ever sat across from an investor who said "we'll do a SAFE" and nodded like you already knew what that meant, this is for you. Convertible notes and SAFEs are not interchangeable. The mechanics differ in ways that affect your cap table for years after the check clears.
What both instruments share
Both are ways to take early investment without setting a company valuation at the time of the check. Instead, they convert to equity at a later round—typically a series A or large seed—at terms set today. That's valuable when your company is early enough that a formal valuation discussion would be speculative at best and harmful at worst.
Both typically include a valuation cap, which limits how high the conversion price can go (protecting the investor), and often a discount rate, which gives the investor a lower conversion price than new investors pay at the next round. That's where the similarity ends.
How convertible notes work
A convertible note is debt. It has an interest rate, a maturity date, and the legal standing of a loan. If you don't raise a priced round before the maturity date, the noteholder has rights that equity investors don't—they can demand repayment, negotiate extended terms, or in some cases force a conversion.
For most early-stage companies, the maturity date is treated as a formality. It isn't. If you hit year three without a priced round, a noteholder can apply real pressure. That's leverage they have by design.
The interest rate also accrues, meaning the total amount that converts to equity at the priced round is your original principal plus accumulated interest. Small in practice, but not zero.
How SAFEs work
Y Combinator introduced the SAFE (Simple Agreement for Future Equity) in 2013 to remove the debt mechanics. A SAFE has no maturity date, no interest rate, no obligation to repay. It converts to equity at the next priced round, full stop.
For founders, this is cleaner. No clock running. No interest accruing. No scenario where an investor can come back and demand payment.
The post-money SAFE—the current standard from YC—also fixes the dilution calculation at signing rather than at conversion. That makes it easier to know exactly what percentage you've sold.
The cap table implications
Stacking multiple SAFEs before a priced round creates a dilution event that all hits at once. If you've raised $2M across six SAFEs and then close a Series A, all six SAFEs convert simultaneously. The cap table math can be more dilutive than it looked when each individual SAFE was signed.
With convertible notes, the conversion also happens at the priced round, but founders are more likely to model it carefully because of the debt framing. The irony is that SAFEs often lead to more casual cap table management because they feel lighter.
When each instrument makes sense
Convertible notes make more sense when the investor expects a priced round within 12-18 months and wants the maturity date as a backstop, when the jurisdiction requires debt instruments for regulatory or tax reasons, or when both parties want the legal protections that come with a creditor relationship.
SAFEs make more sense when you're raising at a stage where a 24-36 month runway is more realistic, when you want simplicity and low legal cost (a SAFE can close for minimal fees with standard docs), or when you're doing a rolling close and want consistent terms across multiple investors.
Most early-stage founders should default to SAFEs. The debt mechanics of a convertible note introduce complexity that rarely benefits founders at the pre-seed stage. See how Alder structures its initial investment on the terms page.
What Alder uses
At Alder, we structure our initial investment as post-money SAFEs with a valuation cap tied to reasonable milestone-based conversion assumptions. We don't use maturity dates as pressure mechanisms. If you're still building toward product-market fit, we're not going to force a conversation about repayment.
That said, we've seen founders mismanage SAFE stacks. If you've raised on three SAFEs at different caps and you're about to close a priced round, you need to know exactly how dilutive that conversion will be before you negotiate the term sheet. If you don't have that number, build it now.
If you're thinking about your first external check and want to work through the structure before you start talking to investors, we're the right conversation to have first. A founder who understands their cap table cold is harder to surprise—and harder to pressure—than one who's fuzzy on the mechanics.