What does $500,000 on a $5,000,000 post-money cap really cost a founder? The answer is 10% of the company, measured right before the next priced round. That one division is the heart of SAFE dilution.
This guide explains how a SAFE turns cash into shares, and how several SAFEs stack up. It also shows why a Series A shrinks every slice, and how a cap and a discount compete for the lower price.
- On a post-money SAFE, the ownership sold equals the investment divided by the valuation cap.
- Stacked post-money SAFEs add their percentages, and the founders absorb all of that dilution.
- The priced round then dilutes everyone, including the SAFE holders, by the same proportion.
- With both a cap and a discount, the investor converts at whichever price is lower.
How a SAFE Turns Cash Into Shares
A SAFE is a Simple Agreement for Future Equity. Y Combinator created it in 2013 as a replacement for convertible notes. The investor pays now and receives shares later, when the company raises a priced round.
The SEC investor bulletin stresses one point above all others. A SAFE is not common stock and is not a current equity stake. It is a promise of future shares that depends on a trigger event.
Two terms decide how many shares the investor finally gets. The valuation cap is the highest valuation at which the SAFE converts. The discount gives the investor a lower price than new investors pay, such as 20% off.
Y Combinator names three events in its user guide: a priced round, a sale of the company, or a dissolution. The SEC warns that some SAFEs never trigger at all. A company that never raises again and is never sold leaves the SAFE unconverted.
How Much of the Company Does One SAFE Take?
On a post-money SAFE, divide the investment by the post-money valuation cap. A $500,000 SAFE on a $5,000,000 cap sells 10% of the company before the priced round.
Y Combinator made the post-money SAFE its standard in 2018. Its SAFE page gives this example: $1 million on a $6.7 million post-money cap sells about 15%. Raising only $500,000 on the same cap sells about 7.5%.
The tool page walks through a smaller case. Maya owns 1,000,000 fully diluted shares and raises $200,000 on a $5,000,000 post-money cap. She sells 200,000 / 5,000,000, which is exactly 4%.
Shares come next. The new total is 1,000,000 / (1 – 0.04), or 1,041,666.67 shares. The SAFE price is $5,000,000 / 1,041,666.67, which is $4.80. At that price, $200,000 buys 41,666.67 shares, so Maya keeps 96%.
The key point is the timing. That 4% is locked in when Maya signs. A later SAFE on a different cap cannot shrink this investor’s slice before the round.
The SAFE Note Dilution Calculator handles up to six SAFEs with caps and discounts. It shows the full cap table before and after your round.
Stacking SAFEs Into a Series A
Several post-money SAFEs simply add their percentages together. The priced round then trims every holder by the same share. The tool page uses this stacked case, and each step below matches its numbers.
- Add up the SAFEs. Priya has 10,000,000 shares. A $500,000 SAFE at an $8,000,000 cap sells 6.25%, and a $1,000,000 SAFE at a $10,000,000 cap sells 10%. Together they sell 16.25%.
- Find the shares after conversion. Divide 10,000,000 by (1 – 0.1625). The company now has 11,940,298.51 shares, and Priya’s group holds 83.75%.
- Price the round. The Series A invests $5,000,000 at a $20,000,000 pre-money valuation. The price is $20,000,000 / 11,940,298.51, which is $1.675 per share.
- Issue the new shares. $5,000,000 / $1.675 gives 2,985,074.63 new shares. The total rises to 14,925,373.13 shares.
- Read the final table. Priya’s group owns 67%, SAFE 1 owns 5%, SAFE 2 owns 8%, and the Series A owns 20%.
Look at the founders’ path. The SAFEs cost 16.25 points and the round cost another 16.75 points. The round took the same 20% bite from every holder, so each SAFE also shrank by one fifth.
Older SAFEs work differently. Pre-money SAFEs, the form used before 2018, leave other SAFEs out of the share base. On the tool page’s comparison, a $1,000,000 SAFE at a $10,000,000 cap gets 10% as a post-money SAFE but only 9.09% as a pre-money one.
Cap or Discount: Which Price Wins?
The SAFE converts at whichever price is lower, because a lower price buys more shares. The cap and the discount are never added together.
The tool page shows this with Jonas. He holds 1,000,000 shares and signs one $300,000 SAFE with a $6,000,000 cap and a 20% discount. His Series A brings $3,000,000 at a $12,000,000 pre-money valuation.
The shares after conversion come to 1,052,631.58, so the round price is $11.40. The discount price is 80% of that, or $9.12. The cap price is $6,000,000 / 1,052,631.58, which is $5.70.
The SAFE converts at $5.70 into 52,631.58 shares. After the round, Jonas owns 76%, the SAFE holder owns 4%, and the new investor owns 20%.
What Happens When the Round Prices Below the Cap?
The SAFE then converts at the lower round price. The investor gets more shares than the cap implied. In one example from the Y Combinator user guide, a SAFE expected to deliver 10% converted into 10.3%.
A new option pool adds one more layer. The YC guide says the post-money cap is not “post” a pool created at the priced round. The option pool dilution calculator models that pool on its own.
Where Do SAFE Dilution Estimates Go Wrong?
Most errors come from mixing up which base a percentage uses. The table pairs each trap with a better habit.
| Mistake | Better approach |
|---|---|
| Treating the SAFE percentage as final ownership | Apply the round. Priya’s 10% SAFE ends at 8% after a round that sells 20%. |
| Adding the cap and discount together | Compare the two prices and use the lower one. Jonas’s SAFE uses $5.70, not both. |
| Ignoring whether a cap is pre or post | Ask which form was signed. The same $10,000,000 cap gives 10% post but 9.09% pre. |
| Assuming the cap always applies | Check the round price. A round below the cap price means more shares for the SAFE. |
| Calling a SAFE a loan | Y Combinator treats it as an equity security. The SEC notes it is not current equity either. |
Dilution is only one side of the deal. An investor judges the payoff with return on investment math. A founder weighs it against the months of runway the cash buys, as our guide to small business cash flow management explains.
Try it with your own terms. Enter each SAFE and your round in the SAFE dilution calculator to see every slice before and after conversion.
SAFE Note Dilution: Frequently Asked Questions
How Do You Calculate SAFE Dilution?
On a post-money SAFE, divide the investment by the valuation cap. A $500,000 SAFE on a $5,000,000 cap sells 10% of the company, measured right before the priced round.
Is a SAFE Note the Same as a Convertible Note?
No. A convertible note is debt with interest and a promise of repayment. A SAFE is an agreement for future shares, and Y Combinator created it in 2013 to replace convertible notes.
Do Post-Money SAFEs Dilute Each Other?
No. Each post-money SAFE keeps the percentage fixed at signing. Two SAFEs selling 6.25% and 10% leave the founders with 83.75% before the round.
Does the Series A Dilute SAFE Holders?
Yes. The SAFEs convert right before the round, so the new money dilutes them like everyone else. A round that sells 20% turns a 10% SAFE into 8%.
What Happens With Both a Cap and a Discount?
The SAFE converts at the lower of the cap price and the discount price. With a $5.70 cap price and a $9.12 discount price, it converts at $5.70.
Can a SAFE Get More Than Its Expected Percentage?
Yes. When the round prices below the SAFE price, the SAFE converts at the lower round price. The Y Combinator guide shows a 10% SAFE converting into 10.3%.
What Happens to a SAFE When the Company Is Sold?
A sale is a liquidity event under the YC SAFE. The holder receives the greater of its purchase amount or the as-converted proceeds at the post-money cap.
Can a SAFE Investor End Up With Nothing?
Yes. The SEC warns that a SAFE may never trigger. A company that never raises a priced round and is never sold may leave the SAFE unconverted.
Sources and Further Reading
References Used in This Article
This article explains standard Y Combinator SAFE math for learning only. It is not legal, tax, or investment advice, and your signed documents control the real outcome. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 27, 2026.
Author
Shakeel Muzaffar is the Founder and Editor-in-Chief of MultiCalculators.com, bringing over 15 years of experience in digital publishing, product strategy, and online tool development. He leads the platform's editorial vision, ensuring every calculator meets strict standards for accuracy, usability, and real-world value. Shakeel personally oversees content quality, formula verification workflows, and the platform's commitment to publishing tools that are genuinely useful for students, professionals, and everyday users worldwide.
