A Simple Agreement for Future Equity (SAFE) is a financial instrument created by Y Combinator in 2013 for early-stage startup financing. A SAFE is not debt — it does not accrue interest, does not have a maturity date, and cannot be called by the investor. Instead, it is a contractual right to receive equity in the company at a future priced financing round, typically a Series A or later, at a pre-negotiated price or with a pre-negotiated price advantage. The original SAFE had four variants (cap only, discount only, cap and discount, MFN). The 2018 YC post-money SAFE simplified this to primarily the post-money SAFE with a valuation cap and optional discount. The valuation cap is the maximum pre-money valuation at which the SAFE can convert — if the Series A is at a higher valuation than the cap, SAFE investors convert at the cap price, receiving more shares per dollar than Series A investors. The discount (typically 15-20%) gives SAFE investors a lower conversion price than the Series A round regardless of valuation cap. Conversion mechanics are the most important aspect of SAFE analysis. At a priced round, SAFE investors convert their principal investment into preferred shares at the lower of: the Series A price per share, the SAFE's cap price per share (Cap / Pre-Money Diluted Shares), or the discounted Series A price (Series A price x (1 - discount rate)). The shares received = SAFE Principal / Conversion Price. Post-money SAFEs (the 2018 YC standard) specify the valuation cap as post-money (after the SAFE itself is included in the company's valuation), giving investors a clear ownership percentage at the time of signing. If an investor puts $250,000 into a startup on a $5M post-money SAFE, they immediately know they will own approximately $250,000 / $5,000,000 = 5% on a fully diluted basis at conversion (assuming no additional SAFEs with the same or lower cap). This transparency is a key advantage of the post-money SAFE. Pre-money SAFEs (the pre-2018 version) used a pre-money valuation cap, making ownership percentage uncertain at signing because the investor's ultimate ownership depends on how many other SAFEs and shares exist at the time of conversion — which is unknown at the time the SAFE is signed. Multiple pre-money SAFEs can interact in complex ways that surprise both founders and investors at the priced round.
Safe Note Calc Calculation: Step 1: Determine the SAFE terms: principal amount, valuation cap (pre-money or post-money), and discount rate (if any). Step 2: At the trigger event (priced round), determine the Series A price per share: Pre-Money Valuation / Pre-Money Fully Diluted Shares. Step 3: Calculate the cap-based conversion price: Valuation Cap / Pre-Money Fully Diluted Shares at the time of the Series A. Step 4: Calculate the discount-based conversion price (if applicable): Series A Price x (1 - Discount Rate). Step 5: The SAFE converts at the lower of the cap-based and discount-based conversion prices (more favorable to the investor). Step 6: Calculate shares received: SAFE Principal / Conversion Price. Step 7: Calculate the SAFE investor's post-conversion ownership: Shares Received / (Total Post-Round Fully Diluted Shares). Each step builds on the previous, combining the component calculations into a comprehensive safe note result. The formula captures the mathematical relationships governing safe note behavior.
- 1Determine the SAFE terms: principal amount, valuation cap (pre-money or post-money), and discount rate (if any).
- 2At the trigger event (priced round), determine the Series A price per share: Pre-Money Valuation / Pre-Money Fully Diluted Shares.
- 3Calculate the cap-based conversion price: Valuation Cap / Pre-Money Fully Diluted Shares at the time of the Series A.
- 4Calculate the discount-based conversion price (if applicable): Series A Price x (1 - Discount Rate).
- 5The SAFE converts at the lower of the cap-based and discount-based conversion prices (more favorable to the investor).
- 6Calculate shares received: SAFE Principal / Conversion Price.
- 7Calculate the SAFE investor's post-conversion ownership: Shares Received / (Total Post-Round Fully Diluted Shares).
When Series A valuation is below SAFE cap, SAFE converts at Series A price — no cap benefit.
The SAFE has a $6M valuation cap. The Series A is priced at $3M pre-money with 10M fully diluted shares, giving a per-share price of $3M / 10M = $0.30. The cap-based price would be $6M / 10M = $0.60. Since the Series A price ($0.30) is lower than the cap price ($0.60), the SAFE converts at the Series A price (the lower of the two — more favorable to the investor). Shares received: $500,000 / $0.30 = 1,666,667 shares. The SAFE investor receives the same price as Series A investors in this scenario — the valuation cap only helps the investor when the Series A valuation exceeds the cap.
SAFE investor pays 2.5x fewer dollars per share than Series A investors — the cap benefit.
The Series A is priced at $15M / 10M = $1.50/share. The cap-based conversion price is $6M / 10M = $0.60/share. Since the cap price ($0.60) is lower than the Series A price ($1.50), the SAFE converts at $0.60. Shares received: $500,000 / $0.60 = 833,333 shares. If the SAFE investor had invested at Series A terms, they would receive $500,000 / $1.50 = 333,333 shares. The cap benefit provides 833,333 - 333,333 = 500,000 additional shares — effectively increasing the SAFE investor's return by 2.5x versus late-stage investors. This is the core value proposition of the SAFE: early-stage risk is rewarded with a better conversion price at the later priced round.
Series A price = $10M / 8M = $1.25/share; discounted price = $1.25 x 0.80 = $1.00/share.
A discount-only SAFE gives the investor a fixed percentage discount off the next round's price, without the ceiling protection of a valuation cap. The Series A price is $10M / 8M = $1.25/share. The 20% discount reduces the SAFE conversion price to $1.25 x 0.80 = $1.00/share. Shares received: $250,000 / $1.00 = 250,000 shares. Without the discount, at the Series A price of $1.25, the investor would receive 200,000 shares — the 20% discount provides 50,000 additional shares (25% more shares for the same investment). Discount-only SAFEs are less common than cap SAFEs because the benefit is limited — if the Series A is at a very high valuation, the 20% discount does not fully compensate for the risk taken at the early stage.
Total new shares from SAFEs: 1.318M added to 9M pre-round + Series A shares.
When multiple SAFEs convert simultaneously at a Series A, each converts independently based on its own cap. Series A price: $12M / 9M = $1.33/share. SAFE1 cap price: $4M / 9M = $0.44/share (below $1.33, so cap applies). SAFE1 shares: $300K / $0.44 = 675,000 shares. SAFE2 cap price: $7M / 9M = $0.78/share (below $1.33, so cap applies). SAFE2 shares: $500K / $0.78 = 643,000 shares. Total SAFE shares: 1.318M. These SAFE shares, combined with the new Series A shares, dilute all pre-existing common shareholders. Note that each SAFE uses the pre-SAFE share count (9M) to calculate the cap price — they do not dilute each other at conversion, though they collectively dilute the founders significantly.
Pre-seed and seed financing for early-stage startups, representing an important application area for the Safe Note Calc in professional and analytical contexts where accurate safe note calculations directly support informed decision-making, strategic planning, and performance optimization
Bridge financing between priced rounds without adding debt, representing an important application area for the Safe Note Calc in professional and analytical contexts where accurate safe note calculations directly support informed decision-making, strategic planning, and performance optimization
Calculating SAFE conversion shares to update cap table at Series A, representing an important application area for the Safe Note Calc in professional and analytical contexts where accurate safe note calculations directly support informed decision-making, strategic planning, and performance optimization
Investor due diligence: reviewing existing SAFE obligations before leading a round, representing an important application area for the Safe Note Calc in professional and analytical contexts where accurate safe note calculations directly support informed decision-making, strategic planning, and performance optimization
Comparing SAFE terms across multiple investors to negotiate the best deal, representing an important application area for the Safe Note Calc in professional and analytical contexts where accurate safe note calculations directly support informed decision-making, strategic planning, and performance optimization
{'case': 'SAFE Conversion in Acquisition', 'description': 'If a company is acquired before raising a priced round, SAFEs typically provide investors the choice of receiving their investment back (as if debt) or converting to equity at the cap price and participating in the acquisition proceeds. Which option is better depends entirely on the acquisition price relative to the valuation cap.'}
Companies incorporated in other jurisdictions (UK, Canada, Singapore) may use adapted versions (like the UK's ASA — Advanced Subscription Agreement) that achieve similar economic outcomes within their local legal frameworks. The tax and legal implications vary significantly by country."}
In the Safe Note Calc, this scenario requires additional caution when interpreting safe note results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when safe note calculations fall into non-standard territory.
| Term | YC Standard | Common Variation | Notes |
|---|---|---|---|
| Valuation Cap | Post-money | Pre-money (older SAFEs) | Post-money gives clearer ownership |
| Discount Rate | None (cap only) or 20% | 15-20% | Discount alone rare; usually paired with cap |
| Interest Rate | 0% (not debt) | N/A | Convertible notes have 4-8% interest |
| Maturity Date | None | N/A | Convertible notes typically 12-24 months |
| Pro-Rata Rights | Side letter (optional) | Often in side letter | Allows investors to follow in Series A |
| MFN Clause | Only in no-cap SAFEs | Sometimes added | Gives early investors most favorable terms |
| Minimum Round Size | $1M qualified financing | Often higher for larger SAFEs | Triggers conversion event |
How is a SAFE different from a convertible note?
A SAFE (Simple Agreement for Future Equity) and a convertible note are both instruments that convert to equity at a later priced round, but they have key structural differences. A convertible note is debt: it carries an interest rate (typically 4-8%), has a maturity date (typically 12-24 months), and if not converted before maturity, the company must repay the principal plus interest or negotiate an extension. A SAFE is not debt: it has no interest rate, no maturity date, and cannot be called by the investor — it simply sits on the balance sheet until a conversion event occurs. SAFEs are simpler to document, have no ongoing interest cost, and eliminate the risk of a maturity event forcing a premature round or repayment. Convertible notes are sometimes preferred by investors in states or jurisdictions where SAFE tax treatment is less certain.
What is a valuation cap and why does it matter?
A valuation cap is the maximum pre-money valuation at which a SAFE or convertible note can convert to equity. It protects investors who funded the company early (at higher risk) from being treated the same as later investors who invested at a higher valuation. If a SAFE investor has a $5M cap and the Series A is at $20M pre-money, the SAFE investor converts at the $5M cap price — receiving 4x more shares per dollar than Series A investors. The valuation cap creates the investor's upside in early-stage investing: the more the company's value grows between the SAFE and the priced round, the more valuable the cap becomes. From the founder's perspective, a low cap means significant dilution if the company grows substantially before the Series A.
What is the YC post-money SAFE and how is it different?
Y Combinator introduced the post-money SAFE in October 2018 to address a transparency problem with the original pre-money SAFE. The original SAFE used a pre-money valuation cap, making it difficult for investors to know their exact ownership percentage at signing because it depended on how many other SAFEs and shares existed at conversion — which was unknown at signing. The post-money SAFE specifies the cap as a post-money valuation (after the SAFE is included), giving investors a clear ownership percentage immediately: Principal / Post-Money Cap = Ownership %. For a $250K SAFE at a $5M post-money cap, the investor knows they will own approximately 5% regardless of other factors. This clarity benefits both investors (known ownership) and founders (easier to explain and track total SAFE dilution).
When does a SAFE convert to equity?
A standard YC SAFE converts to equity upon a Qualified Financing — defined as a priced round of at least a specified minimum amount (typically $1M or more). At conversion, the SAFE investor receives preferred shares at the conversion price (lower of cap price or discount price). SAFEs also contain provisions for conversion upon a Liquidity Event (acquisition, merger, or IPO) — if the company is acquired before a priced round, SAFE investors typically receive their invested amount or the equivalent value at the acquisition price, whichever is greater. Dissolution events also trigger rights: if the company shuts down, SAFE investors have priority over common stockholders to receive any remaining assets up to their investment amount.
What is a most-favored-nation (MFN) clause in a SAFE?
A Most Favored Nation (MFN) clause in a SAFE gives the investor the right to receive any more favorable terms offered to future SAFE investors. If a startup sells a SAFE with an MFN clause at a $5M cap, and later sells another SAFE at a $3M cap, the MFN investor can elect to adopt the $3M cap. MFN clauses are designed to protect investors who signed first (and took the highest risk) from being disadvantaged if the startup later offers better terms to subsequent investors. They are most common in SAFEs without a valuation cap (pure MFN SAFEs) — the investor gets no cap now, but if a later investor gets a cap, the MFN investor can adopt it.
How much equity does a SAFE investor receive?
The equity received by a SAFE investor depends on the principal amount, the valuation cap (or discount), and the capitalization at the time of conversion. For a post-money SAFE, the calculation is straightforward: SAFE Principal / Post-Money Valuation Cap = approximate ownership percentage at conversion (before accounting for the dilution from the SAFE itself and other SAFEs). For example, $500K on a $5M post-money cap = ~10% ownership. For pre-money SAFEs, the calculation is more complex because the ownership depends on the pre-money diluted share count at the time of conversion, which changes as the option pool and other instruments are added. SAFE investors receive preferred shares with the same rights as other preferred investors in the same series.
Are SAFEs taxed differently from convertible notes?
The tax treatment of SAFEs and convertible notes differs primarily at the time of issuance and conversion. For investors, convertible note interest is taxable income when received. SAFEs have no interest component, so this tax issue does not arise. When SAFEs and notes convert, investors receive preferred stock — typically not a taxable event for either party. For founders, selling SAFEs or notes does not create immediate taxable income (unlike receiving services in exchange for equity). The tax complexity arises when SAFEs convert in conjunction with an option pool or other equity issuances — consult a tax attorney for large SAFE transactions or when SAFEs convert with unusual terms. The IRS has provided limited formal guidance on SAFE taxation, making professional advice essential for complex situations.
Pro Tip
Y Combinator updated the standard SAFE from post-money to post-money SAFE (2018) — the post-money SAFE gives investors a known ownership percentage at signing, which is cleaner and more transparent for both parties. Always clarify which version of the SAFE is being used.
Did you know?
Y Combinator introduced the SAFE (Simple Agreement for Future Equity) in late 2013 as a replacement for convertible notes. SAFEs are now used in the vast majority of pre-seed and seed financings in the US, and YC's standard SAFE documents are available for free on their website — one of the most significant contributions to startup ecosystem accessibility.