A convertible note is a short-term loan that converts into equity at a future priced round instead of being repaid in cash. It's the earlier, debt-based version of what a SAFE does more simply.
Because it's structured as debt, a convertible note carries an interest rate and a maturity date, and it sits above equity holders if the company is liquidated. Like a SAFE, it usually has a valuation cap and/or a discount, so early investors get a better effective price than whoever prices the next round.
The maturity date is the real difference from a SAFE. If a priced round hasn't happened by then, the note is technically due and repayable, which puts pressure on both the company and the investor to extend it or force a conversion event. Most notes get amended rather than called, but it's a real deadline a SAFE simply doesn't carry.
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