As a founder, you may be wondering how to choose between SAFE or convertible notes for your startup. Pre-SAFE (pre-money) notes are diluted by all funding and notes that occur before the maturity date. Post-SAFE (post-money) notes are only diluted by the funding round that triggers conversion. Pre-SAFE notes lead to less dilution for the founders and more dilution for the note holders while Post-SAFE notes lead to the opposite. Pre-SAFE notes are more difficult to calculate ownership when there are more investors and notes compared to Post-SAFE notes. In general, the reason to go with a note is a shorter time period to receive seed funding and lower associated cost, though the cost of a priced equity round has come down.
Convertible Notes are a debt instrument that convert into equity at either a qualifying event or at the maturity date. They also accrue interest (compounded annually) which converts into equity as well. Their conversion is pre-money so they will be diluted by other notes and other funding pre-Series A. Though it is rare for a convertible note to be repaid at the maturity date and are generally extended.
The interest on the note leads to more dilution.