Convertible Notes vs SAFEs: Which to Use

A SAFE (Simple Agreement for Future Equity) and a convertible note both let a startup raise a bridge round without pricing the company today - the money converts into equity later, at a discount or valuation cap, once a priced round happens. The difference is what's underneath the paperwork: a SAFE is not debt, carries no interest, and has no maturity date, while a convertible note is a debt instrument that accrues interest and must be repaid or renegotiated if it matures before a priced round. This guide walks through both instruments' mechanics, a worked conversion example, and how to decide which one to use.

Founders raising a pre-seed or seed round, and investors writing early checks, both want the same thing: get money into the company fast without spending weeks negotiating a priced valuation. SAFEs and convertible notes both solve this, but they allocate risk differently between the company and the investor. Getting the mechanics wrong - especially around valuation caps, discounts, and what happens at maturity - is one of the most common and costly mistakes in early-stage fundraising.

Both instruments delay pricing the company until a future round - the real difference is what happens if that round never comes.

What Is a SAFE?

A SAFE, created by Y Combinator in 2013, is a contract that gives an investor the right to receive equity in the future, in exchange for cash today. It is explicitly not a loan: there is no interest rate, no maturity date, and no obligation for the company to repay the investor if a priced round never happens. The investor is betting entirely on the company eventually raising a priced round (or getting acquired), at which point the SAFE converts into preferred shares.

Because a SAFE has no interest or maturity mechanics to negotiate, the paperwork is short (Y Combinator's standard templates run 5-6 pages) and legal costs are low. That simplicity is the main reason SAFEs have become the default instrument for pre-seed and seed rounds in the US.

What Is a Convertible Note?

A convertible note is a debt instrument. Like a SAFE, it converts into equity at a future priced round, discount, or cap - but unlike a SAFE, it is a loan first: it accrues interest (typically 4-8% annually) and has a maturity date (typically 18-24 months). If the company hasn't raised a priced round by maturity, the note holder technically has the right to demand repayment or force a renegotiation of terms, which gives noteholders real leverage that SAFE holders don't have.

Convertible notes predate SAFEs and are still common outside Silicon Valley, in jurisdictions where SAFEs are less standard, or when investors specifically want the downside protection that comes with a real debt claim.

The Core Economic Terms: Valuation Cap and Discount

Both instruments typically carry one or both of the following terms, which determine the price at which the investment converts into shares:

• Valuation cap: The maximum effective valuation at which the instrument converts, regardless of the priced round's actual valuation. A lower cap is more favorable to the investor - it guarantees them a cheaper price per share if the company's value has grown a lot by the time it prices a round.
• Discount rate: A percentage discount (typically 15-25%) off the price per share that new investors pay in the priced round.

When both a cap and a discount are present, the instrument converts at whichever price is lower - i.e., whichever gives the SAFE or note holder more shares for their money.

// Conversion price per share
= MIN(ValuationCap / FullyDilutedShares, SeriesA_PricePerShare * (1 - Discount))

// Shares issued (SAFE)
= Investment / ConversionPrice

// Shares issued (convertible note, includes accrued interest)
= (Principal + AccruedInterest) / ConversionPrice

Worked Example: SAFE vs. Convertible Note Conversion

Assume a company has 5,000,000 fully diluted shares outstanding before its Series A, and it raises that Series A at a $10,000,000 pre-money valuation - a Series A price per share of:

Series A Price per Share = $10,000,000 / 5,000,000 shares = $2.00

The company also has two bridge instruments outstanding, both for a $500,000 investment with a $5,000,000 valuation cap and no discount, issued 14 months before the Series A closes:

Cap price per share (same for both, since the cap is identical):

Cap Price per Share = $5,000,000 / 5,000,000 shares = $1.00

Since $1.00 is lower than the $2.00 Series A price, both instruments convert at the $1.00 cap price rather than the Series A price.

SAFE conversion:

Shares Issued = $500,000 / $1.00 = 500,000 shares

Convertible note conversion (the note has accrued interest that the SAFE does not):

Accrued Interest = $500,000 × 6% × (14 / 12) = $35,000
Total Owed = $500,000 + $35,000 = $535,000
Shares Issued = $535,000 / $1.00 = 535,000 shares

The note holder ends up with 35,000 more shares than the SAFE holder for putting in the identical $500,000 - purely because of the 14 months of accrued interest. This is the economic cost of the note's downside protection: the company gives up more equity in exchange for the investor bearing the risk of a debt instrument.

Full post-round cap table, assuming a new Series A investor puts in $3,000,000 at the $2.00 Series A price ($3,000,000 / $2.00 = 1,500,000 new shares):

(Percentages are rounded to one decimal place and may not sum to exactly 100.0% due to rounding.)

Pre-Money vs. Post-Money SAFEs

In 2018, Y Combinator switched its standard SAFE from a pre-money to a post-money structure, and post-money is now the market default. The distinction matters enormously for dilution math:

• Pre-money SAFE: The valuation cap is applied before the SAFE money itself is added, so the SAFE holder's ownership percentage is diluted by every other SAFE issued in the same round.
• Post-money SAFE: The valuation cap is applied after the SAFE money is added, which means the SAFE holder's percentage ownership is fixed and known at signing - it isn't diluted by other SAFEs stacked on top before the priced round.

Post-money SAFEs are easier for an investor to reason about (their exact ownership percentage is locked in immediately), but they can surprise founders who stack several post-money SAFEs without tracking the cumulative dilution each one implies. Always confirm which structure a term sheet uses before comparing caps across instruments.

Interest and Maturity: Where Notes Diverge from SAFEs

The worked example above shows the mechanical difference interest makes, but maturity is the more consequential divergence in practice. A SAFE has no maturity date - if the company never raises a priced round or gets acquired, the SAFE simply sits on the balance sheet indefinitely (or converts under whatever fallback provisions the specific SAFE version includes).

A convertible note's maturity date is a real deadline. If the company hasn't triggered a conversion event by then, the note holder can, in principle, demand repayment of principal plus accrued interest - which most early-stage companies cannot do without raising more cash. In practice, this usually forces a renegotiation (extending the maturity date, converting at a fixed price, or converting to a bridge-priced round) rather than an actual cash repayment, but it hands the noteholder real negotiating leverage that a SAFE holder never has.

Which Should Founders Use?

For most US pre-seed and seed rounds, a SAFE is the default choice: it's faster to close, cheaper in legal fees, and doesn't create a repayment obligation or maturity deadline hanging over the company. Investors have largely converged on this norm, so using a SAFE also signals you're following standard market practice.

A convertible note makes more sense when:

• Investors specifically require the downside protection (and negotiating leverage) that comes with debt.
• You're raising outside the US, where SAFEs are less standardized or not recognized the same way under local law.
• The round includes institutional investors who prefer the priority-of-claim that debt provides in a wind-down scenario.

Whichever instrument you choose, model every outstanding SAFE and note's cap, discount, and (for notes) accrued interest in your cap table before you negotiate the priced round - stacking several instruments with different caps can create dilution surprises that aren't obvious until you actually run the conversion math.

Common Mistakes

1. Not tracking the blended dilution of multiple SAFEs. Three SAFEs at three different caps convert at three different prices - model each one separately, not as a single blended pool.
2. Ignoring accrued interest on notes when estimating dilution. As the worked example shows, interest measurably increases the noteholder's share count; skipping it understates dilution to founders.
3. Confusing pre-money and post-money SAFE caps. The two structures imply materially different founder dilution when several SAFEs are stacked - always confirm which one you're using.
4. Letting a note mature without a plan. A maturity date that arrives before a priced round forces a renegotiation under time pressure; track maturity dates and start the conversation with noteholders well before the deadline.
5. Treating a SAFE cap as "free" upside for the company. A low valuation cap is a real cost - it fixes a cheap conversion price for the investor no matter how much the company's value grows before the priced round.
6. Forgetting MFN (most-favored-nation) clauses. Some SAFEs and notes include a clause letting the holder claim better terms from any later instrument issued before conversion - this can quietly reprice every earlier SAFE in the stack.