SAFE Dilution Calculator

What Is a SAFE?

A SAFE (Simple Agreement for Future Equity) is the most common instrument for early-stage startup fundraising. Created by Y Combinator in 2013, it lets investors give you money now in exchange for the right to receive equity later — typically when you raise a priced round. Unlike convertible notes, SAFEs have no interest rate, no maturity date, and no repayment obligation.

Pre-Money vs Post-Money SAFEs

The key difference is how dilution is allocated:

• Post-money SAFE (YC standard since 2018): The valuation cap includes all SAFE holders. This means each investor knows exactly what percentage they're buying — it's simply their investment amount divided by the cap. All dilution comes from the founders, not from other SAFE investors.
• Pre-money SAFE: The valuation cap only covers existing shares. Multiple SAFEs dilute each other, making it harder for any investor (or the founder) to know their exact ownership until conversion.

Most investors and accelerators now use the post-money SAFE because it's clearer and more predictable.

How Valuation Caps Work

A valuation cap sets the maximum price at which the SAFE converts into equity. If your company is valued at $50M in your Series A but the SAFE had a $10M cap, the SAFE investor converts at the $10M valuation — getting 5x more shares per dollar than the new investors. The cap protects early investors from overpaying if the company grows significantly before the priced round.

How Dilution Works

When SAFEs convert, new shares are created for the SAFE holders. This increases the total share count, which reduces (dilutes) everyone else's percentage ownership. With a post-money SAFE at a $10M cap and a $1M investment, the investor will own 10% of the company — meaning the founders' percentage drops by 10 percentage points.

Multiple SAFEs stack. Three investors each putting in $500K on a $10M post-money cap each get 5%, for a total of 15% dilution. This is why tracking your SAFE stack matters — founders are often surprised by the cumulative dilution when everything converts at the Series A.

Common Mistakes Founders Make

• Not tracking cumulative dilution: Each SAFE feels small on its own, but stacking multiple SAFEs with low caps can leave founders with surprisingly little ownership.
• Confusing pre-money and post-money: A $500K investment on a $5M pre-money cap is very different from a $5M post-money cap. The post-money version means exactly 10% dilution; the pre-money version depends on what other SAFEs exist.
• Ignoring the option pool: Your Series A investors will likely require expanding the option pool before conversion, further diluting founders on top of the SAFE conversion.
• Setting caps too low: A low cap feels good because it means more money from investors, but it also means more dilution. Founders sometimes optimize for valuation cap as a vanity metric without modeling the actual ownership impact.
• Not modeling the full picture: Use a tool like this calculator to see what your cap table will look like after all SAFEs convert. Better to know now than be surprised at your Series A closing.