Founders raising pre-seed money almost never read the cap table math before they sign, and that single habit is what quietly costs them the most equity.
Here's what actually happens at a pre-seed closing: the lawyer sends a template, the founder skims it for the check size and the deadline, and nobody runs the numbers on what a 20% discount stacked against a $6 million cap actually does to the founder's ownership eighteen months later. The convertible note vs SAFE decision gets made by whichever document a lawyer happens to have on file, not by which one is cheaper for the person who built the company. That's backwards, and it's fixable with about ten minutes of arithmetic.
Both instruments do the same basic job. They let an investor hand you money now in exchange for stock later, once a priced round sets an actual valuation. Neither is stock. Neither requires you to agree on what the company is worth today, which is the whole point: pre-seed companies are notoriously hard to price, and forcing that conversation early usually just wastes everyone's time in negotiation.
Y Combinator created the SAFE, short for Simple Agreement for Future Equity, in late 2013, and it's now the default instrument at pre-seed across most of Silicon Valley. A SAFE is not a loan. It carries no interest rate and no maturity date, which means there's no clock forcing repayment or renegotiation if the company hasn't raised a priced round yet. The investor hands over cash, gets a contractual right to shares later, and simply waits.
That waiting is the entire design philosophy. Carta, which tracks cap tables for tens of thousands of startups, has reported that SAFEs now account for the majority of pre-seed financing documents on its platform, largely because YC pushed the template into wide use and lawyers stopped billing hours to redraft it from scratch. A SAFE typically runs two to four pages. A note, with its interest provisions and default terms, usually runs longer and costs more in legal fees to negotiate.
The mechanism is a conversion trigger, not a repayment date. When you raise a priced Series A, the SAFE converts into equity at whichever is more favorable to the investor: the discount rate applied to the new round's price, or the valuation cap. Nothing converts until that trigger fires, so if you never raise a follow-on round, the SAFE just sits there.
Convertible Note Explained: The Loan That Wants to Become Equity
A convertible note is a debt instrument first and an equity instrument second. It accrues interest, usually 2% to 8% annually, and it carries a maturity date, typically 18 to 24 months out. If the company hasn't raised a priced round by maturity, the note technically comes due, and the investor can demand repayment or force a conversion at the cap even without a new financing event. That's a real difference in leverage, and it's the reason lawyers built notes with maturity provisions in the first place: they give the investor a backstop if the company stalls.
Interest matters more than founders think. A $500,000 note at 6% interest that sits for two years before converting adds roughly $60,000 in accrued interest, and that interest converts into shares too, at the same discount or cap as the principal. You're not just diluting for the money you raised. You're diluting for the cost of the money sitting unconverted.
The Discount Rate and the SAFE Valuation Cap, Worked Through
This is where the real dilution math lives, and it's the part almost nobody runs before signing. Say you raise $500,000 on a SAFE with a $5 million valuation cap and a 20% discount. Eighteen months later you raise a Series A at a $20 million pre-money valuation. The investor doesn't convert at $20 million. They take the better of the two: the cap gives them a $5 million effective valuation, the discount gives them $16 million (20% off $20 million). The cap wins by a wide margin, so your seed investor ends up owning shares priced as if the company were worth $5 million, in a company that just proved it's worth four times that.
Now push the cap down to $3 million on the same round. That investor's $500,000 buys them roughly 16.7% of the company at conversion math, versus around 10% at the $5 million cap. A $2 million difference in the cap, negotiated in a single afternoon over email, can mean six or seven points of founder ownership permanently gone. Multiply that across a stack of SAFEs from an angel round, a pre-seed round, and a bridge, and the cap table math compounds in ways spreadsheet-averse founders rarely see coming until the Series A term sheet lands and the fully diluted count looks nothing like they expected.
Stack too many notes and SAFEs with different caps and discounts, and you get what lawyers call a conversion waterfall: each instrument converts in whatever order the documents specify, and the earliest, lowest-cap money often ends up owning a disproportionate share relative to what it actually contributed. Carta's own data on seed-stage cap tables has flagged this stacking problem repeatedly, since founders who raise on a rolling SAFE close for a year often don't realize how many different caps are layered into the same round until a lawyer builds the pro forma ahead of the priced round.
Which One Actually Costs You More
Neither instrument is inherently worse. A SAFE with no interest and no maturity date is friendlier to the founder in isolation, and that's exactly why YC built it that way. But investors have caught up. Many now insist on lower caps or steeper discounts on SAFEs precisely because they're giving up the interest and the maturity leverage a note would give them. You often end up paying for that flexibility somewhere else on the term sheet.
The instrument matters less than the numbers inside it. A note with a $8 million cap and no discount can be cheaper than a SAFE with a $4 million cap and a 25% discount, depending entirely on where your next round prices. Don't ask your lawyer which template to use. Ask them to model your fully diluted ownership under two or three realistic Series A scenarios before you sign anything, because that's the only version of this conversation that actually tells you what you're giving away.
Also read: How to Read a Startup Term Sheet Before You Sign It • What Is a Vesting Schedule in Startup Equity and Crypto Token Deals • How Vesting Schedules Work for Startup Founders and Employees and How to Negotiate Yours
