SAFEs and convertible notes get lumped together as "early-stage instruments that turn into equity later," and founders often sign whichever one their lawyer hands them without asking what changes at the moment of conversion. That moment is where the differences actually cost you something.
A note is debt. A SAFE isn't.
A convertible note has an interest rate and a maturity date, because it's legally a loan. If you haven't raised a priced round by the maturity date, noteholders can technically demand repayment — money you almost certainly don't have sitting in the bank. A SAFE has no maturity date and no interest; it simply waits until a priced round happens, however long that takes. If your timeline to a priced round is uncertain, that difference alone should decide which instrument you use.
Interest means more shares, quietly
Because notes accrue interest, noteholders convert more shares than the dollar amount they originally invested — the interest becomes additional principal that also converts. Founders are often surprised at close by how much more dilution the notes caused versus what they mentally budgeted for.
Stacking caps from multiple rounds gets messy fast
If you raise on a SAFE at a $5M cap, then again at an $8M cap, then again at a $12M cap, all three convert at their own cap in the same priced round — meaning the earliest investors get the best price, exactly as intended, but your total dilution from three "small" bridge raises can be larger than founders expect going in. Model all outstanding SAFEs and notes together before your next priced round, not just the newest one.
The question to ask your lawyer
Not "which one is standard" — ask "walk me through exactly what my cap table looks like the day this converts, assuming a $10M priced round." If they can't answer that in the same meeting, you don't understand the instrument well enough to sign it yet.