Startup equity calculator: see the dilution by round.

Model a simple cap table, one SAFE and four-year vesting with a one-year cliff — free, no sign-up.

ExampleTwo founders with 10 million shares, a $500K post-money SAFE capped at $10M, and a $5M seed at $20M pre-money — illustrative numbers. Replace them with your cap table.

Educational model only — not financial or legal advice. Your signed financing documents govern conversion and vesting. Review the cap table with qualified advisors.

Initial holders (name,shares per line)

One SAFE before round 1 (optional)

SAFE investment (USD; 0 disables)Post-money valuation cap (USD; 0 uncapped)SAFE discount (%)

Cap and discount use the more favorable conversion price. This configurable combination is not a claim that it matches an unmodified YC SAFE. Review the actual instrument.

Round 1

Round 1 nameRound 1 pre-money USDRound 1 new investment USD

Illustrative vesting: 4 years, 1-year cliff

Vesting grant (shares)Elapsed whole months

The grant is a separate illustration; it does not add shares to the cap table. Before month 12: zero. At month 12: 25%. Monthly thereafter to month 48.

Formulas and assumptions

S = initial fully diluted shares; I = SAFE investment; C = post-money cap; V = first-round pre-money; d = discount fraction.

E = min(C, V × (1 − d)), ignoring C when uncapped. q = I / E. SAFE shares = S × q / (1 − q). SAFE price = I / SAFE shares.

Round price = V / shares before new money. New shares = new investment / round price. Round dilution = new investment / (V + new investment). The theoretical dilution is investment / (V + investment); actual ownership uses emitted whole shares.

Vesting = 0 before month 12; otherwise grant × min(months, 48) / 48. New SAFE and round shares are rounded down; the fractional remainder is discarded. Ownership is recalculated from emitted whole shares; displayed percentages sum to 100%.

One SAFE only, converted before the first round. V includes converted SAFE shares. No pool increase, other SAFEs, notes, fees, interest or pro-rata rights. A pre-money SAFE or different capitalization definition needs another model.

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Educational model only — not financial or legal advice. Your signed financing documents govern conversion and vesting. Review the cap table with qualified advisors.

Equity formulas and assumptions

Educational model only — not financial or legal advice. Your signed financing documents govern conversion and vesting. Review the cap table with qualified advisors. Single SAFE; pre-money includes converted shares. Vesting grant is separate.

Equity formulas and assumptions
Calculation	Formula / limit
SAFE valuation	E = min(cap, pre-money × (1 − discount)); ignore zero cap
SAFE ownership	q = investment / E, before new money
SAFE shares	initial shares × q / (1 − q)
Theoretical round dilution	investment / (pre-money + investment), before whole-share rounding
Vesting	0 before month 12; grant × min(months,48)/48 thereafter
Excluded	Pools, other SAFEs, notes, fees and pro-rata rights

How to use

Enter initial holders and shares, then optional SAFE investment, post-money cap and discount. Zero investment disables it.
Enter up to six priced rounds in order and a separate vesting grant with whole elapsed months.
Inspect each cap table and formula, then export JSON for review with your advisors.

Reference documentation

Y Combinator SAFE documents — checked 2026-10-09 ↗

Frequently asked questions

Is it free, and is an account required?

Free, no sign-up. Editing and exports run in your browser without an AI model. Usage events contain only the tool name and action. Drafts last while the page is open; download before leaving.

What SAFE model is used?

One SAFE before round one. E = min(cap, pre-money × (1 − discount)); ignore cap if uncapped. q = investment / E; SAFE shares = initial shares × q / (1 − q). Pre-money includes converted SAFE shares. Investment must be below E.

Is cap and discount the standard YC SAFE?

No. This configurable model chooses the favorable cap or discount. YC publishes separate forms. Capitalization definitions, pools, other SAFEs and pro-rata rights can change results. This is an educational model, not a contract interpreter.

How do rounds dilute holders?

Price/share = pre-money / shares before new money. New shares = investment / price. Theoretical new investor stake = investment / (pre-money + investment). Emitted shares are rounded down; actual ownership is recalculated from whole shares and display percentages sum to 100%.

How does vesting work?

Monthly over 48 months with a 12-month cliff: zero before month 12, 25% at month 12, then grant × min(months,48)/48. This grant is separate from the cap table and adds no shares to it.

What is excluded?

Multiple or pre-money SAFEs, note interest, pool increases, fees, pro-rata rights, acceleration. Newly issued shares are rounded down and the fraction discarded; ownership uses emitted whole shares and displayed percentages sum to 100%. Signed documents and qualified advisors govern financing.

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