SAFE Note Conversion: The Complete Guide for Startup Founders
Understand exactly how Y Combinator SAFE notes convert at a priced round. Learn the 4 SAFE types, see real calculations, and model your own conversion.
What Is a SAFE Note?
A SAFE (Simple Agreement for Future Equity) is an investment instrument created by Y Combinator in 2013. It's designed to be a simple alternative to convertible notes — no interest, no maturity date, and no need to figure out valuation at the time of investment.
Key Point: A SAFE is NOT equity — it's a promise to give investors equity when you raise a future priced round (typically a Series A or seed equity round).
When that priced round happens, the SAFE "converts" into shares. The question is: at what price per share? That's where things get interesting (and sometimes confusing).
The 4 YC SAFE Types
YC offers four standard SAFE templates. The key difference between them is how the conversion price is calculated:
| SAFE Type | Conversion Price | Best For |
|---|---|---|
| Cap Only | Cap / Pre-Money Valuation | Founders confident in future valuation |
| Discount Only | Priced Round Price × (1 - Discount) | When cap is hard to determine |
| Cap + Discount | Lower of Cap or Discount price | Most common — investor protection |
| MFN (Most Favored Nation) | Best terms from any future SAFE | Early investors who want flexibility |
Conversion Basics: How SAFEs Convert
Before diving into each type, let's establish the fundamental formula:
The Shares Issued is what varies by SAFE type. Once we have the conversion price, we can calculate ownership:
SAFE with Valuation Cap
A valuation cap is the maximum price per share the SAFE investor will pay. If your company does better than expected, the cap protects the investor. If it does worse, the investor shares in the downside.
Example: You raise a $1M SAFE with a $10M cap. Later, you raise a priced round at a $20M pre-money valuation.
Conversion Price Calculation:
With a cap-only SAFE, the conversion price is:
Wait — that's not quite right. Let's be more precise. The conversion price per share is:
In practice, we usually calculate shares directly:
Real Numbers:
| Item | Value |
|---|---|
| SAFE Investment | $1,000,000 |
| SAFE Cap | $10,000,000 |
| Priced Round Pre-Money | $20,000,000 |
| Pre-Money Shares | 10,000,000 |
| SAFE Shares Issued | 1,000,000 |
| SAFE Ownership | 4.76% |
Why this works: The SAFE investor effectively bought 10% of the company at a $10M valuation (their cap), even though the company is now worth $20M. Their ownership is diluted by the new money coming in.
SAFE with Discount
A discount SAFE gives investors a percentage discount on the priced round price. The most common discount is 20%.
Example: You raise a $500K SAFE with a 20% discount. Later, you raise at $2/share.
| Item | Value |
|---|---|
| SAFE Investment | $500,000 |
| Discount | 20% |
| Priced Round Price | $2.00/share |
| SAFE Conversion Price | $1.60/share |
| SAFE Shares | 312,500 |
SAFE with Both Cap and Discount
This is the most common SAFE type. It gives investors the lower of two conversion prices — either the cap price or the discounted price. Investors get the best of both worlds.
Example: You raise a $1M SAFE with a $10M cap AND 20% discount. Priced round is at $20M pre-money.
Calculate Both, Take the Lower:
Cap Price Calculation:
At $10M cap, the SAFE would buy 10% of the pre-money.
Discount Price Calculation:
20% discount on the priced round price.
The winner? In this case, the cap wins (gives the investor a better deal).
Watch out: Sometimes the discount wins! If your priced round is close to the cap, the 20% discount might actually be better for the investor than the cap. Always calculate both.
The MFN SAFE
MFN stands for "Most Favored Nation." This SAFE is simple: it says "whatever the best terms are for any future SAFE investor, I get those too."
Example: Angel Alice invests $100K via MFN SAFE. Two months later, Angel Bob invests $200K with a $10M cap + 20% discount. Alice's SAFE now has those same terms.
MFN SAFEs are typically used by early investors who want to get in quickly but don't want to negotiate terms yet.
Multiple SAFEs: The Waterfall
Most startups have multiple SAFEs. When conversion happens, all SAFEs convert using the same methodology — but the order matters for some calculations (like option pool allocation).
Important: All SAFEs convert based on the pre-money valuation of the priced round. The new investment money doesn't dilute SAFEs — SAFEs dilute each other and founders.
Example: 3 SAFEs Converting
| SAFE | Amount | Terms | Shares | Ownership |
|---|---|---|---|---|
| Safe #1 | $500K | $8M Cap | 625,000 | 2.38% |
| Safe #2 | $750K | $10M Cap | 750,000 | 2.86% |
| Safe #3 | $1M | 20% Discount | 625,000 | 2.38% |
| TOTAL | $2.25M | 2,000,000 | 7.61% |
Assumes 10M pre-money shares, priced round at $20M pre-money, $2/share.
Common Mistakes to Avoid
- Confusing pre-money vs post-money cap: In 2018, YC introduced a "post-money" SAFE. The math is different. Know which version you have!
- Forgetting option pools: Option pools typically come out of the pre-money, diluting both founders AND SAFEs.
- Assuming MFN is free: MFN SAFEs can become expensive if you later offer generous terms to other investors.
- Not modeling the waterfall: When you have multiple SAFEs with different terms, calculate each one separately.
Model Your SAFE Conversion
Use our free SAFE Note Calculator to see exactly how your SAFEs will convert at your next round. Supports all 4 YC SAFE types and multiple SAFEs.
Try SAFE Calculator →Calculate Your SAFE Conversion
Understanding SAFE conversion is crucial for both founders and investors. The math can get complex quickly, especially with multiple SAFEs and different terms.
Use FounderMath's SAFE Calculator to:
- Model all 4 YC SAFE types
- Handle multiple SAFEs in one round
- See the conversion waterfall
- Calculate exact ownership percentages
- Generate shareable scenarios
Pro tip: Before you sign a SAFE, run the numbers. A $1M difference in cap might not seem like much now, but it could mean 2-3% more dilution at your Series A.
Use our free SAFE Note Calculator to model how your SAFEs convert at your next priced round. No signup required.
Try SAFE Note Calculator Free →