Founders & Small BusinessFree tool
SAFE and Note Conversion Calculator
Every SAFE and note you've signed, converted together against your next priced round, in one cap table showing what you and each investor own.
Free to start · Opens in your River workspace, ready to edit and share
How to calculate SAFE and convertible note conversion
SAFE and convertible note conversion is the math that turns each instrument into shares at your next priced round. A post-money SAFE buys at least a set slice of the pre-round company: the investment divided by its valuation cap. A note usually converts at the lower of its cap price and its discounted round price, and its interest can convert too. Convert them all first, because the round's price depends on the converted total. Then the round's new money and new option pool dilute founders and SAFE holders alike.
The rule that matters most: post-money SAFE percentages add up. Y Combinator, which created the SAFE, notes that five $100,000 SAFEs at a $5 million cap sell 10% of the company, not 2%1. No single document shows the total, so keep a running sum.
Gather the terms from the signed documents
Work from the signed SAFEs, notes and side letters, not from emails or an old spreadsheet. You also need the fully diluted count just before the round: issued shares, granted and promised options, and the unissued pool. If that count is shaky, rebuild it first with a cap table template.
What to pull from each document
| Document | Terms that change the math | Watch for |
|---|---|---|
| Post-money SAFE | Purchase amount, valuation cap, any discount | Its cap includes all SAFE money, not the round's money or new pool |
| Pre-money SAFE | Purchase amount, pre-money cap, any discount | An older form whose holders dilute each other |
| MFN SAFE | Purchase amount, and the dates it was signed and funded | Any later SAFE whose better terms it can adopt |
| Convertible note | Principal, interest rate and start date, maturity, cap, discount, minimum round size | Whether interest converts, and which share count the cap divides |
| Side letter | Pro rata rights, MFN rights | Shares an investor can buy in the new round |
Add up what your SAFEs have sold
For each post-money SAFE, divide the investment by the valuation cap. In YC's own example, $500,000 at a $5.5 million cap is about 9%, and $500,000 at an $8.3 million cap is about 6%2, so together they sell about 15%.
A slice doesn't shrink when you sign more SAFEs, because every SAFE's math already counts the others. YC's user guide puts it simply: "The safes are like their own round."3 The priced round's new money and new option pool then dilute them along with the founders.
Older pre-money SAFEs are harder: they dilute each other and count the next round's pool increase, so their slice isn't known until then. If you've issued both kinds, YC says you'll need to run the conversion calculations for all of the outstanding safes3.
Watch for an MFN SAFE
An uncapped MFN SAFE can adopt the terms of a SAFE you sign later. If an angel's $250,000 MFN picks up a later $5 million cap, it buys 5% before the round. YC's advice: close lower-cap SAFEs before you issue an uncapped MFN2.
Convert notes with their interest
A convertible note is debt, so it carries interest and a maturity date. YC says note interest is often 2% to 8%1. Peter Werner, a partner at the law firm Cooley, writes that interest can be simple or compounding, and paid in cash or converted into shares4.
Next, compare two prices. Cooley explains that a note's cap and discount usually work "in the alternative"4: the note converts at whichever gives the lower price. The same primer puts typical discounts at 15% to 25%. A 20% discount only wins when the round's share price is below 1.25 times the cap price.
Take a $300,000 note at 5% simple interest, converting after two years: $330,000 converts. If its cap price is $0.66 a share and the round price less 20% is $0.96, it converts at $0.66, into 500,000 shares.
Many notes also convert automatically only in a round above a minimum size, which Cooley says is typically one to two times the notes' principal4. And past its maturity date, a note can come due for repayment.
Calculate the conversion and the round price
Term sheets normally count converting SAFEs and notes inside the pre-money valuation, and YC's user guide calls leaving them out a negotiated exception3. So your SAFEs don't shrink the new investor's stake; the existing holders absorb them.
The new option pool usually sits in the pre-money too. Venture capitalist Brad Feld wrote that investors who want a bigger pool will insist that such increase happen prior to the financing5, which effectively lowers the true pre-money valuation.
Solve the post-money SAFEs
Take the fully diluted count before the round, plus any shares from notes or pre-money SAFEs. Divide it by 1 minus the SAFEs' combined percentage, and give each SAFE its slice.
Size the new pool
If the pool must be a set percentage after closing, take the converted count less any unissued options. Divide it by 1 minus the new investors' and the pool's percentages for the post-round total, and take the pool's share of that.
Set the price
Divide the pre-money valuation by the converted count plus the shares added to the pool. The new money buys shares at that price.
Check every cap
If a SAFE's cap price is above the round price, or a note's discount beats its cap, convert that one at the lower price and rerun.
Before the round: 9,000,000 fully diluted shares, 8,000,000 of them the founders' (88.9%) and 1,000,000 granted options.
SAFEs: $500,000 at a $5 million post-money cap and $1,000,000 at a $10 million cap, 10% each.
Converted: 9,000,000 ÷ 0.80 = 11,250,000 shares. Each SAFE gets 1,125,000, and the founders hold 71.1%.
Series A: $4 million at a $16 million pre-money, with a 10% pool after closing. Post-round total: 11,250,000 ÷ 0.70 = 16,071,429 shares, including a new pool of 1,607,143.
Price: $16,000,000 ÷ 12,857,143 = $1.2444 a share. The founders end at 49.8%, each SAFE at 7.0%, options at 6.2%, the pool at 10% and the Series A at 20%.
- The pool is in the pre-money. Worth $2 million at the round price, it leaves existing holders a $14 million pre-money, not $16 million.
- Both caps bind. Cap prices of $0.44 and $0.89 sit below the $1.24 round price, so both SAFEs convert at their caps.
YC's own worked example3 follows the same steps: two SAFEs selling 15% and a $5 million Series A take the founders from 92.5% to 51.54%.
Read the result before you sign
Divide each check by the percentage points it holds after the round. In the example, the $500,000 SAFE paid $71,429 a point, the $1,000,000 SAFE $142,857 and the Series A $200,000. The fewer dollars per point, the more that money cost you.
Then rerun the model with a better round and a worse one. Cooley calls it critically important that founders run through a sensitivity analysis4 when deciding how much to raise and where to set the cap. A round priced near or below your caps gives SAFE and note holders more shares than the caps imply.
Count pro rata rights too. The round has to make room for the new investors and for existing investors with pro rata rights. If you haven't planned for that, YC warns, you may end up taking more dilution than you anticipated3.
Once the ownership is right, read the rest of the deal with a term sheet explainer, and see what each stake pays in a sale with an exit waterfall analysis.
Have a lawyer confirm the mechanics
The SAFE math here follows YC's standard US forms. Modified SAFEs, notes and side letters vary, and only the signed documents decide how they convert. Have a startup lawyer check your numbers before you sign a term sheet.
Before you sign the term sheet
- Every SAFE, note and side letter is in the model, with its signed terms
- The post-money SAFE percentages add up to a total you have checked
- Note interest runs to the expected closing date
- Each MFN is modeled at the terms it could adopt
- The new pool matches the term sheet: its size, and whether it sits in the pre-money
- Founder ownership is shown for a better and a worse round
The calculator at the top of this page runs these steps from your own documents. It converts every SAFE and note at once and lists any term it couldn't confirm.
How it works
Start with the SAFEs and notes you've signed, your cap table and the round you expect. River reads each instrument's terms from what you share, converts them all together and writes a converted cap table and a short summary into your workspace. You see what the founders own before and after the round, and what each check cost per point.
Anything it can't confirm from the signed documents, like a missing side letter, is marked for you to check instead of guessed. River does the arithmetic; your lawyer confirms how your specific documents convert.
List what you signed
Paste or describe every SAFE, note and side letter, plus your cap table and the round you expect.
River converts everything
It reads each instrument's terms, applies any MFN elections and converts them all together against one round.
Get your cap table
A sheet with the converted cap table and scenarios, plus a summary of who owns what afterward.
Test other rounds
Edit any term, model a different round size or valuation, or ask which terms are still worth negotiating.
What you get
- Every SAFE, note and side letter listed by funding date, with its cap, discount and interest
- A converted cap table with one row per holder, showing shares and percentages that total 100%
- Whether each instrument converts at its cap or its discount, and the valuation where they cross
- The cost per point of ownership for every check, with the most expensive money named
- MFN elections and the new option pool on their own lines, with what each costs the founders
- Each founder's ownership before and after your round, plus a better and a worse scenario
Common questions
How does a SAFE convert in a priced round?
A SAFE converts automatically into preferred stock at your next priced round, with no minimum raise needed. A post-money SAFE converts at its cap price, the cap divided by the fully diluted count just before the round, SAFEs included. If the round's own price gives more shares, it uses that instead. At the cap, holders get a shadow series: the new investors' rights at a lower price.
How do I convert my SAFEs and notes with River?
Type or paste your SAFEs, notes and side letters, your cap table and the round you expect into the box at the top of this page. Attach the signed documents if you have them. River converts every instrument together and writes a converted cap table and a short summary into your free River workspace, marking any term it couldn't confirm.
Does the valuation cap or the discount apply?
Whichever gives the holder the lower price per share, decided separately for each instrument at the round's price. With a 20% discount, the discount wins only when the round prices shares below 1.25 times the cap price. So the cap governs in a round priced well above it, and the discount in one priced near or below it.
What happens to an MFN SAFE at conversion?
It converts at the priced round's own price, into the same shares the new investors buy, unless its holder has already adopted a later SAFE's terms. An uncapped MFN SAFE lets the investor amend it to match a later SAFE with a cap or discount they prefer, usually only once. The amended SAFE copies that later SAFE whole, so the investor can't mix terms from several.
How is a convertible note different from a SAFE?
A note is debt: it accrues interest, has a maturity date and is repaid before SAFE holders if the company is sold or wound down. At conversion it works much like a SAFE with a cap and a discount. The differences are that its interest can convert too, and many notes convert only in a round above a minimum size.
Why does the new option pool cost founders so much?
Because investors usually want the new pool created before the round, inside the pre-money valuation. Its shares then dilute the founders and post-money SAFE holders, but not the new investors. A 10% pool in a round with a $20 million post-money is worth $2 million, which comes out of what the existing holders' shares are worth.
Is the SAFE and note conversion calculator free?
Yes, it is free to start. Your converted cap table opens in a River workspace, where you can edit it, share it or ask River to change it. Paid plans add more AI use and access to the most advanced models.
Sources
Y Combinator. “SAFE vs. convertible note vs. priced round.” ycombinator.com (opens in a new tab)
Y Combinator. “The SAFE — the open standard for startup fundraising.” ycombinator.com (opens in a new tab)
Y Combinator. “Post-Money Safe User Guide.” bookface-static.ycombinator.com (opens in a new tab)
Cooley GO. “Primer on Convertible Debt.” cooleygo.com (opens in a new tab)
Feld Thoughts. “Term Sheet: Price.” feld.com (opens in a new tab)
Built by
Chandler Supple
Co-founder & CEO, River
Chandler has spent the last six years working in AI, building tools for millions of users and Fortune 100 companies. In 2025, he co-founded River to build a new kind of operating system for AI agents.