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Startup Equity Calculator: How to Calculate Ownership Through Each Round

To calculate startup ownership through rounds, start from fully diluted shares, convert each SAFE at its own price, add any option pool top-up the new investor requires, then issue the new investor's shares at the round price. Your ownership is your shares divided by the post-closing fully diluted total. Order matters, because each step changes the denominator for the next.

What an equity calculator actually computes

A startup equity calculator answers one question: what percentage of the company does each holder own after a given sequence of financings. It does not answer what that percentage is worth. Value at exit depends on liquidation preferences, future rounds, and the sale price, which is a separate waterfall calculation.

The percentage that matters is fully diluted ownership: your shares divided by every share outstanding plus every option granted, every option reserved in the unissued pool, and every convertible instrument on an as-converted basis. Founders who divide by issued shares alone overstate their position, because the pool and the instruments are already claims on the company.

The inputs a calculator must ask for

A calculator that skips any of these produces a confident wrong answer.

  • Current share counts. Common held by each founder, options granted, and the unissued pool.
  • Each SAFE. Amount, valuation cap, discount, whether it is pre-money or post-money, and any most favoured nation clause.
  • Each convertible note. Principal, interest rate and accrual date, cap, and discount, since accrued interest usually converts too.
  • The priced round. New money and the pre-money valuation.
  • The pool requirement. Target size, and whether it is measured pre-money or post-money.
  • Pro rata participation. Existing investors buying into the round change the new investor allocation.

The order of operations also has to be right: SAFE conversion, then pool top-up, then the new investor's shares, solved together because each depends on the others.

Worked example: two SAFEs, a pool top-up, and a priced round

All figures are illustrative, chosen to show the mechanics. They are not market benchmarks. The example assumes standard post-money SAFEs with a valuation cap and no discount.

Starting position

Two founders hold 4,000,000 common shares each, 8,000,000 in total. The company has a 1,000,000 share option pool: 200,000 options granted to an early employee and 800,000 unissued. Fully diluted shares are 9,000,000.

Founders together own 88.9 percent. The employee owns 2.2 percent.

Step 1: the SAFEs

The company raises 500,000 dollars on a post-money SAFE capped at 8 million dollars, which buys 6.25 percent, and later 1,000,000 dollars capped at 10 million dollars, which buys 10 percent. Each percentage is measured against the company capitalization at conversion, including the SAFE shares themselves.

So the SAFE holders take 16.25 percent of a capitalization that includes them. The existing 9,000,000 shares become 83.75 percent of the total, which is 10,746,269 shares. The first SAFE converts into 671,642 shares and the second into 1,074,627 shares, at implied prices of about 0.744 and 0.931 dollars.

Founders now own 74.4 percent. Notice that the second SAFE diluted the founders, not the first SAFE holder.

Step 2: the priced round and pool top-up

A lead invests 3,000,000 dollars at a 15 million dollar pre-money valuation, 18 million post-money, so the new investor buys one sixth, or 16.67 percent. The term sheet requires an unissued pool of 10 percent of the post-closing company, created before the round.

Solving the three steps together, the pool needs 556,309 new shares, taking the unissued pool to 1,356,309. The pre-money fully diluted count becomes 11,302,578 shares, so the price per share is about 1.327 dollars, and the investor receives 2,260,516 shares. The post-closing total is 13,563,094 shares.

The result

  • Founders: 8,000,000 shares, 58.98 percent, or 29.49 percent each.
  • Early employee: 200,000 options, 1.47 percent.
  • First SAFE holder: 4.95 percent.
  • Second SAFE holder: 7.92 percent.
  • Unissued pool: 10.00 percent.
  • New investor: 16.67 percent.

Had the round required no pool top-up, the founders would have ended at 62.0 percent. The pool requirement cost them about three points, which is why pool size is negotiated as hard as price.

Where calculations usually go wrong

Pre-money and post-money SAFEs mixed. A pre-money SAFE's percentage moves with everything else that converts. Modelling one as the other misstates founder dilution.

The pool in the wrong place. A pool measured post-money but modelled pre-money, or the reverse, shifts several points between founders and the investor.

MFN clauses ignored. An uncapped SAFE with a most favoured nation clause takes the best later terms. Add a lower-cap SAFE and the earlier one converts on it too.

Note interest left out. Accrued interest on convertible notes usually converts, adding shares.

Rounding. Shares are whole numbers. A model that rounds percentages instead of share counts will disagree with the legal record.

Calculating an employee's ownership

For an employee, the calculation is the same: options or shares divided by the company's fully diluted total. Ask the company for that total, not just the grant size. A grant of 200,000 options means 2.2 percent or 1.5 percent depending on which side of the round the question is asked, as the example shows.

The calculator stops at percentages. Equity grants, vesting, and conversions have legal and tax consequences, and this is general information under US practice, not legal or tax advice. Have counsel review the documents.

Frequently asked questions

How do I calculate my equity percentage in a startup?
Divide the shares or options you hold by the company's fully diluted share count, which includes all issued shares, granted options, the unissued option pool, and convertible instruments on an as-converted basis. Ask the company for the fully diluted total. Your grant size alone says nothing about your percentage.
How do SAFEs affect founder ownership?
When a SAFE converts, the company issues new shares to the holder, which reduces everyone else's percentage. With post-money SAFEs, each holder's percentage is fixed before the priced round, so every additional SAFE dilutes the founders and other common holders rather than earlier SAFE holders.
What is an option pool top-up and who pays for it?
A new investor often requires the unissued option pool to reach a target size, such as 10 percent of the post-closing company. If the new shares are added before the round, in the pre-money, the founders, existing holders, and converting SAFE holders absorb the dilution and the new investor does not.
Is an equity calculator the same as valuing my shares?
No. A calculator gives ownership percentages after each financing. What those percentages pay depends on the exit price, liquidation preferences held by investors, further dilution, and for options the exercise cost and taxes. Treat ownership as the first input to a value estimate, not the estimate itself.