SAFE Note Dilution Calculator
See exactly how much ownership you keep when your SAFE notes convert. Enter your current shares, each SAFE amount with its cap or discount, and your priced round terms. You get conversion prices, new share counts, and a full ownership table before and after the round. All math runs in your browser.
A SAFE dilution calculator shows how much of your company SAFE holders receive when their investment converts at your next priced round. Enter existing shares, each SAFE amount, valuation cap, and discount, plus Series A terms. You get each SAFE conversion price, shares issued, and full cap table ownership before and after the round.
How This SAFE Note Dilution Calculator Works
The calculator models one question: after my SAFEs convert and my priced round closes, who owns what? Fill in the three blocks below, then read your results in the next card. Everything recalculates as you type.
What Your SAFE Dilution Results Mean
Enter at least one SAFE amount with a cap or discount, plus your existing share count. A priced round is optional.
It follows the standard Y Combinator SAFE forms, but your signed documents and any side letters control the real outcome. Ask a startup lawyer before you close a round. See the full limitations section.
SAFE Dilution Formulas and Conversion Rules
SAFE dilution is ownership math with three moving parts: the SAFE terms, the shares on your cap table today, and the price of your next round. The rules below follow the official Y Combinator SAFE forms and user guide. One quick language note: people say "SAFE note," but a SAFE is not a note or a loan. It has no interest and no maturity date.
Post-Money SAFE Conversion Formula
On a post-money SAFE, the ownership you sell is fixed the moment you sign: investment divided by the valuation cap. That percentage holds right before the priced round converts everyone, no matter how many other SAFEs you add.
The shares behind that percentage come from the conversion price, which divides the cap by the company capitalization. The company capitalization includes all shares, options, the existing option pool, and every converting SAFE and note. It excludes the new round money and any new pool created with the round.
Because every SAFE sits in every other SAFE's denominator, stacked post-money SAFEs add up cleanly. Founders, not earlier SAFE holders, absorb all SAFE dilution.
How Cap and Discount Conversion Prices Work
A SAFE converts at the lowest price it is entitled to, because a lower price means more shares for the investor. The three possible prices are the cap price, the discount price, and, in one edge case, the round price itself.
Example: a $6,000,000 cap produces a $5.70 cap price, while a 20% discount on a $11.40 round price produces a $9.12 discount price. The SAFE converts at $5.70, so the cap wins here. A discount-only SAFE, with no cap, uses the discount price alone, which is why it needs round terms before it can calculate.
Series A Price per Share
The round price decides how many shares the new investor gets, and it feeds the discount price above. SAFEs convert immediately before the priced round, so the standard convention prices the round on the share count after SAFE conversion plus any new option pool.
If your term sheet prices the round on the share count before SAFE conversion instead, your real dilution will differ from this model. That is rare with post-money SAFEs, but it is worth asking your lawyer which convention your round uses.
Pre-Money SAFE Conversion (Legacy Safes)
Signed before late 2018, pre-money SAFEs divide the cap by a smaller denominator: your shares, options, existing pool, and the new pool from the round. Other SAFEs and convertible notes are left out. That changes the story in two ways.
First, you cannot know your true dilution when you sign, because later SAFEs land on top of the same base. Second, at the same dollar cap, a pre-money SAFE issues fewer shares than a post-money one. A "$10M pre" cap is simply worth less to the investor than a "$10M post" cap. The comparison table in your results shows both frameworks side by side.
SAFE Dilution Examples With Step-by-Step Math
These three examples match the preset buttons above, so you can load each one and check every number yourself. All three use post-money SAFEs, the current standard.
Example 1: Single SAFE With a Valuation Cap
Maya owns 1,000,000 fully diluted shares and raises $200,000 on a $5,000,000 post-money cap, with no priced round yet.
Maya signs knowing she sold exactly 4%. No later SAFE on a different cap can change that investor's slice before the round.
Example 2: Stacked SAFEs Into a Series A
Priya has 10,000,000 shares and two SAFEs: $500,000 at an $8,000,000 cap and $1,000,000 at a $10,000,000 cap. She then raises a $5,000,000 Series A at a $20,000,000 pre-money valuation.
Priya's group went from 100% to 67%. The SAFEs cost 16.25 points and the round cost another 16.75, because everyone who owned shares before the round took the same 20% hit.
Example 3: SAFE With Cap and Discount
Jonas holds 1,000,000 shares and signs one $300,000 SAFE with a $6,000,000 cap and a 20% discount. His Series A is $3,000,000 new money at a $12,000,000 pre-money valuation.
The cap and discount are not added together. The investor simply gets whichever price is lower. In this round the cap protected the investor, which is typical when valuations rise between signing and conversion.
Pre-Money vs Post-Money SAFE Dilution
The framework decides who eats the dilution when you stack SAFEs. With post-money SAFEs, each investor's percentage is locked at signing and founders absorb everything new. With pre-money SAFEs, each conversion leans on the same share base, so the final split only becomes clear at the round.
Here is the same deal under both frameworks: 10,000,000 existing shares, a $1,000,000 SAFE at a $10,000,000 cap, then a $5,000,000 round at $20,000,000 pre.
| Measure | Post-money SAFE | Pre-money SAFE |
|---|---|---|
| SAFE shares at conversion | 1,111,111 | 1,000,000 |
| SAFE ownership before the round | 10.00% | 9.09% |
| SAFE ownership after the round | 8.00% | 7.27% |
| Existing holders after the round | 72.00% | 72.73% |
| Round price per share | $1.80 | $1.8182 |
Share counts rounded for display. Percentages use exact values.
At the same cap number, the pre-money SAFE costs the founder less, and the gap widens as you stack more SAFEs. When you compare term sheets, always ask whether a cap is quoted pre or post. Your results card computes both versions of your inputs automatically.
Nearby tools on this site solve different questions, so this page stays focused on convertible dilution. Our ROI calculator measures return on a completed investment, not equity conversion. The business calculators hub lists every other planning tool we publish.
Limitations of This SAFE Calculator
This tool models standard Y Combinator SAFE forms converting in a priced equity round. Real deals can differ, so treat every output as an estimate and read this list before acting on a result.
- Legal and tax decisions need professionals. This is an educational model. Your signed documents, side letters, and local law control the real outcome.
- MFN and uncapped SAFEs are not modeled. Every SAFE entered here needs a cap, a discount, or both. An uncapped MFN SAFE only settles once you know the best terms issued later.
- Mixed stacks are approximated. The framework switch applies to all rows at once. A true stack mixing pre-money and post-money SAFEs has a third set of math this page does not attempt.
- Liquidity events use different rules. Acquisitions, IPOs, and dissolutions follow payout rules in the SAFE that this tool does not model.
- Pricing conventions vary. The model prices the round after SAFE conversion plus any new pool, per the YC user guide. Some term sheets price the round on the pre-SAFE share count instead.
- Whole shares and edge terms. Real closings round to whole shares and may add warrants, advisory shares, or pro-rata purchases that shift the final table by small amounts.
- Insight thresholds are editorial rules of thumb. The color bands in the Result Insight are our plain-language guideposts, not industry standards.
SAFE 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. Add up every SAFE the same way, then apply the round's dilution to whatever is left for the founders.
Do SAFEs dilute each other?
Not under post-money SAFEs, the standard since 2018. Each SAFE's percentage is fixed at signing, and founders absorb all dilution from later SAFEs. Under the older pre-money form, SAFEs stacked on the same share base, so the final split depended on how much you raised in total.
What if a SAFE has both a cap and a discount?
The investor converts at whichever price is lower: the cap price or the round price minus the discount. A lower price buys more shares. In most rising rounds the cap wins, because it was set when the company was worth less.
What happens if the round price is below my SAFE cap?
The SAFE converts at the lower round price instead of the cap price, which gives the investor more shares than the cap implied. Y Combinator's user guide shows this case: an investor expecting 10% ended up with about 10.3% because the round priced below the safe price. The calculator applies this rule automatically.
Do SAFE notes charge interest or have a maturity date?
No. A SAFE is not debt. Y Combinator created it in 2013 to replace convertible notes, so it pays no interest and never comes due. It converts at a priced round, a liquidity event, or a dissolution, whichever happens first.
Can this calculator handle stacked SAFEs at different caps?
Yes, up to six SAFEs, each with its own amount, cap, and discount. Stacked post-money SAFEs add their percentages directly, so two SAFEs selling 8% and 10% leave the founders with 82% before the round dilutes everyone.
Sources and Methodology
Sources
Y Combinator, "The SAFE: the standard way startups raise money." Official SAFE forms, the 2018 switch to post-money, cap and discount definitions, and the ownership formula of amount divided by cap. ycombinator.com/documents
Y Combinator, "Post-Money Safe User Guide" (Primer v1.1). Company capitalization definitions for pre-money and post-money SAFEs, including what each denominator includes and excludes. Download the PDF
Y Combinator, "Safe User Guide" (February 2023). Series price formula of pre-money valuation divided by shares after SAFE conversion plus the option pool increase, and the worked conversion examples this page's test cases mirror. Download the PDF
Wikipedia, "Simple agreement for future equity." Corroborates the 2013 origin by Y Combinator and the no-interest, no-maturity structure versus convertible notes. Read the article
Methodology, Testing, and Privacy
The engine solves all SAFE conversions together with a fixed-point iteration that repeats until share counts change by less than one billionth of a share, which handles the circular math created when SAFEs sit in each other's denominators. Formulas follow the Y Combinator documents above. Every formula was checked against hand-worked cases and the worked examples in the YC user guides.
All calculations run locally in your browser with no network requests, no accounts, and no saved inputs. Units are fixed for this tool: dollar amounts and whole shares, so no metric or US unit switching applies. Found an error? Use our corrections policy or contact page. Our methodology page and editorial policy explain how we build and review tools.
Reviewed for calculation accuracy by the MultiCalculators editorial team.
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.
