What Is a SAFE Agreement?
A SAFE (Simple Agreement for Future Equity) is a contract between a startup and an investor. The investor gives the company money today in exchange for the right to receive equity in the future — typically when the company raises a priced round (like a Series A).
Y Combinator invented the SAFE in 2013 as a simpler, cheaper alternative to convertible notes. It has since become the dominant instrument for pre-seed and seed fundraising in the US, and increasingly in the UK and Europe via SeedLegals.
The key insight: a SAFE is not debt, and it has no maturity date. The investor is not a lender. They hold a promise that converts into equity later — on terms that were agreed upfront.
In plain English: "I'll give you £50,000 now. When you raise your Series A, I'll get shares — calculated using the cap and discount we agreed on today."
How a SAFE differs from selling equity directly
When you issue a SAFE, you don't set a valuation right now. That's the point — early-stage valuations are largely arbitrary. Instead, you defer valuation to your next priced round, when the market has more data to price your company accurately.
This makes SAFEs faster to close (a few days instead of weeks), dramatically cheaper (minimal legal fees), and simpler for both sides. There is no interest accruing, no board seats changing, and no maturity deadline to worry about.
Pre-Money vs Post-Money SAFEs
This is the single most important distinction in SAFE mechanics, and the one most founders misunderstand. Y Combinator updated the standard SAFE to a post-money SAFE in 2018. Almost everyone uses post-money now — but many founders still think in pre-money terms.
The pre-money SAFE (older, less common)
With a pre-money SAFE, the conversion calculates your ownership percentage before the new money from the priced round is counted. This made investor dilution calculations harder — multiple SAFE holders couldn't easily know their final ownership because it depended on how many other SAFEs were also converting at the same time.
The post-money SAFE (current standard)
With a post-money SAFE, the ownership percentage is calculated after all the SAFE investments are included in the calculation. This gives investors a known, predictable ownership target from day one.
| Feature | Pre-Money SAFE | Post-Money SAFE |
|---|---|---|
| Introduced | 2013 | 2018 |
| Investor ownership certainty | Low — depends on total SAFEs | High — fixed at signing |
| Dilution falls on | Founders + all SAFE holders together | Founders first (SAFE holders are protected) |
| Complexity | Harder to model | Straightforward |
| Common use today | Rare (legacy deals) | Standard for new rounds |
⚠ Founder warning: Post-money SAFEs are investor-friendly on dilution. When you stack multiple post-money SAFEs, all that dilution comes out of your ownership first. This is why modelling your cap table before issuing SAFEs matters.
Model pre-money vs post-money SAFEs, stack up to 3 rounds, and see your exact ownership before and after conversion.
Want the full conversion math with worked numbers? Read the deep dive: Pre-Money vs Post-Money SAFE: What Every Founder Gets Wrong — includes three complete dilution examples on a $5M raise with a $20M cap.
Valuation Caps Explained
The valuation cap is the maximum company valuation at which a SAFE investor's money converts into equity. It protects early investors from being diluted if the company grows significantly before the priced round.
How the cap works
Say you raise a SAFE with a £3M cap. Your Series A is priced at a £12M pre-money valuation. Without a cap, the investor would convert at £12M — buying shares at the full Series A price. With a £3M cap, they convert as if the company were worth £3M — a 4× better price per share.
The formula: Shares issued = Investment amount ÷ (Cap ÷ Fully diluted shares before conversion)
Setting the right cap
A cap signals what you think the company is "worth" today, without formally being a valuation. Too low and you're giving away too much equity. Too high and it's not a meaningful protection for investors — they may push back or walk away.
Common ranges at pre-seed in 2026:
- Pre-revenue, idea stage: £1M–£3M cap
- Early traction (first customers): £3M–£6M cap
- Strong traction / MVP live: £5M–£10M cap
Uncapped SAFEs
Some SAFEs are issued without a cap at all, relying only on a discount rate. This is generally only palatable if there's a strong MFN (Most Favoured Nation) clause — which guarantees the investor will get the same terms as whoever gets the best deal in the next SAFE round.
Discount Rates
A discount rate gives SAFE investors the right to convert at a cheaper price than Series A investors — rewarding them for taking on more risk at an earlier stage.
A 20% discount is standard. This means if Series A shares are priced at £1.00, the SAFE investor converts at £0.80 per share.
Cap vs discount: which applies?
When a SAFE has both a cap and a discount, the investor gets whichever gives them more shares — i.e. the lower effective price per share. This is standard and reflects the investor's reward for early risk.
Example: If the cap-based price is £0.50 and the discount-based price is £0.80, the investor converts at £0.50 (the cap wins).
This is exactly the kind of calculation that's tedious to do by hand but takes seconds with the right tool. Our free SAFE Dilution Calculator handles all of this automatically — just enter your cap, discount, and investment amount.
How SAFEs Convert at Series A
SAFEs convert into preferred shares (or ordinary shares, depending on jurisdiction) when a triggering event occurs. The most common trigger is a priced equity round above a minimum threshold — typically £1M+.
The conversion sequence
- Series A is priced. Lead investor sets a pre-money valuation and price per share.
- SAFE holders convert. Each SAFE's investment converts to shares using the lower of: (a) cap-based price, or (b) discount-based price.
- Option pool. If a new option pool is created at the priced round, it's typically drawn from pre-money shares — diluting founders and SAFE holders proportionally.
- New Series A investors buy in. At the full priced round valuation.
What happens if there's no priced round?
SAFEs can also convert on a sale (acquisition) or IPO. Some SAFEs have dissolution provisions that pay out investors if the company winds down. The mechanics vary — read your specific SAFE document carefully.
Important: If you raise multiple SAFEs over time, they all convert at once at the Series A. Stacked SAFEs can mean serious founder dilution. Model it before each raise.
Stack up to 3 SAFEs, add your Series A valuation, and see the full cap table before you agree to anything.
SAFE vs Convertible Note
Before SAFEs existed, convertible notes were the go-to early-stage instrument. Both convert into equity at a later date — but the mechanics differ significantly.
| Feature | SAFE | Convertible Note |
|---|---|---|
| Is it debt? | No | Yes — legally a loan |
| Interest | None | Typically 5–8% p.a. |
| Maturity date | None | Usually 12–24 months |
| Legal complexity | Low — 5-page standard doc | Higher — requires term sheet |
| Legal cost | Very low (standard templates) | Higher (negotiation required) |
| Repayment risk | None | Yes — if no round before maturity |
| Common in | US, growing UK/Europe | UK, Europe (traditional) |
When convertible notes still make sense
Notes still appear in the UK where SEIS/EIS tax relief is involved (which requires shares to be issued), and in deals where investors specifically want debt-like protection. If your investor has a strong preference for a note, understand why — and model both scenarios before agreeing.
Common Mistakes Founders Make With SAFEs
Issuing SAFEs without modelling the cap table
Most first-time founders issue a SAFE, then another, then another — without ever seeing what their fully-diluted ownership will look like at Series A. By the time the round closes, they own 30% less than they expected. Model every SAFE before you sign it.
Setting the cap too low under pressure
Angels and seed funds will push for a low cap. Founders, desperate to close, agree to £1M on a company that has real traction. That's not founder-friendly — a £1M cap on a £10M Series A means 10× dilution before new money even comes in.
Mixing pre-money and post-money SAFEs
If you issued pre-money SAFEs early and are now issuing post-money SAFEs, your cap table maths gets complicated fast. When possible, standardise on one type. For a full breakdown of how each type converts and why the difference matters at Series A, see our deep dive on pre-money vs post-money SAFEs.
Not understanding the option pool shuffle
Series A investors often require a 10–15% option pool to be created before they invest — which means that dilution comes from existing shareholders (founders and SAFE holders), not from the new money. This is the "option pool shuffle" and it can catch founders off guard.
Issuing too many SAFEs to too many angels
Having 20 SAFE holders going into a Series A creates administrative overhead and can spook institutional investors. Where possible, consolidate — either through a SPV (special purpose vehicle) or by keeping the SAFE count manageable.
Using a non-standard template
The YC standard SAFE and the SeedLegals SAFE are widely understood by investors and lawyers. Custom SAFE templates introduce friction, require legal review, and can contain terms that look harmless but aren't. Start with a standard template.
When to Use SAFEs
SAFEs are the right tool in most early-stage situations — but not all. Here's when they work and when they don't.
Use a SAFE when:
- You're raising pre-seed or seed from angels, scouts, or seed funds
- You want to close quickly (days, not months)
- You don't want to set a formal valuation yet
- Your investors are comfortable with a deferred equity structure
- You're raising in tranches from multiple investors over a few months
Consider alternatives when:
- Your investors specifically need SEIS/EIS relief (UK) — requires actual share issuance
- You're raising a larger seed (£2M+) where a priced round may make more sense
- Your investors want voting rights or information rights immediately
- You're in a jurisdiction where SAFEs have unfavorable tax or legal treatment
The practical decision tree
Raising <£500K from angels quickly? SAFE. Raising £1M+ from institutional seed funds with strong opinions? Get legal advice and compare a priced seed round. Raising in the UK with SEIS investors? You likely need shares, not a SAFE.
Bottom line: A SAFE is not always the right tool — but for most pre-seed rounds, it's the fastest and cheapest path. Whatever instrument you choose, model the dilution first. Our free SAFE Dilution Calculator takes under 2 minutes to give you the full picture.