Startup Option Pools: Calculate the Pre-Money Dilution Before You Sign

A pre-money option-pool top-up dilutes founders and existing holders before the financing. To calculate the effect, add the required reserve to the fully diluted pre-money capitalization, recalculate the financing price per share, and only then calculate the investor’s shares.

Do not start with a generic percentage. Build a role-by-role equity budget through the next expected financing, subtract the reserve that remains genuinely available, and solve for the smallest top-up that covers the hiring plan and a defensible contingency.

Why a pre-money pool creates extra dilution

Suppose an investor agrees to invest I at a pre-money valuation V. Without a pool increase, the investor’s post-money ownership is I divided by V plus I. A hypothetical $3 million investment at a $12 million pre-money valuation therefore buys 20% after the financing.

A pre-money pool increase leaves that investor percentage unchanged. The additional reserve enters the fully diluted pre-money denominator, lowering the price per share and shifting the resulting dilution to existing holders. AngelList’s option-pool example uses an $8 million pre-money valuation and $2 million investment: a required 20% post-money pool leaves founders with 60%, the pool with 20%, and the new investor with 20%.

Valuation and pool language therefore need to be evaluated together. A higher headline valuation paired with an oversized pre-money pool can leave founders with less ownership than a lower valuation paired with a smaller reserve.

Build the spreadsheet in the correct order

Start with the capitalization definition in the term sheet. A fully diluted pre-money denominator may include issued shares, outstanding options and warrants, convertible securities, and the existing unallocated reserve. Keep each category on a separate row even when the document combines them for pricing.

For a term requiring the unallocated pool to equal T of post-financing fully diluted capitalization, define:

• S = current fully diluted pre-money shares, including the existing unallocated reserve
• U = currently unallocated and usable reserve shares
• V = pre-money valuation
• I = new investment
• X = additional reserve shares included before the financing
• N = shares issued to the new investor

The spreadsheet-ready solution is X = [T × (1 + I/V) × S − U] / [1 − T × (1 + I/V)]. Then calculate the financing price as V / (S + X), investor shares as I divided by that price, and post-money fully diluted shares as S + X + N.

This formula applies only when T means the unallocated reserve as a percentage of the post-financing fully diluted total and the top-up is included pre-money. A target based on pre-money capitalization, the total equity plan, or a different securities definition needs a different model. Resolve that wording alongside the valuation, investment amount, liquidation preference, and other term-sheet economics.

A complete pre-money top-up example

As a hypothetical example, assume a company has 10 million fully diluted shares before the round: 8 million founder shares, 1 million seed-investor shares, 500,000 outstanding employee options, and 500,000 unallocated reserve shares. It is raising $3 million at a $12 million pre-money valuation, and the term sheet requires the unallocated reserve to equal 10% of post-money capitalization.

Here, S is 10 million, U is 500,000, I/V is 0.25, and T is 0.10. The formula produces 857,143 additional reserve shares when rounded to the nearest share. The expanded pre-money capitalization becomes 10,857,143 shares, and the unallocated reserve becomes 1,357,143 shares.

The financing price is approximately $1.1053 per share, so the investor receives approximately 2,714,286 shares. Post-money capitalization is approximately 13,571,429 shares, producing this ownership:

• Founders: 8,000,000 / 13,571,429 = 58.95%
• Seed investor: 1,000,000 / 13,571,429 = 7.37%
• Outstanding employee options: 500,000 / 13,571,429 = 3.68%
• Unallocated reserve: 1,357,143 / 13,571,429 = 10%
• New investor: 2,714,286 / 13,571,429 = 20%

Without the top-up, the financing alone would leave the founders at 64%. The pre-money pool condition reduces their ownership by another 5.05 percentage points while the investor remains at 20%. That is the incremental cost to isolate before signing.

Compare the same target with post-money treatment

If the company completes the financing first and expands the reserve afterward, the new investor shares the dilution. In the hypothetical example, financing without a top-up creates 2.5 million investor shares at $1.20 per share, producing 12.5 million fully diluted shares before the later increase.

To make the existing 500,000-share reserve equal 10% after a post-money increase, the company adds 833,333 reserve shares: (500,000 + X) / (12,500,000 + X) = 10%. Founders then own 60%, while the investor owns 18.75%. The reserve reaches the same 10% target, but the dilution is distributed differently.

Do not compare the pre-money and post-money cases by looking only at the number of added reserve shares. Compare every holder’s final percentage under the same valuation, investment, securities definition, and pool target.

Separate allocated options from usable capacity

Granted options are not available for new offers. They remain part of fully diluted ownership while outstanding, but they should not be counted as unallocated hiring capacity. Shares may return to the plan after a departure or expired grant if the governing documents provide for it; projected returns are not the same as capacity available today.

Use separate rows for issued shares, granted and outstanding options, approved commitments not yet granted, and the unallocated reserve. An offer letter that mentions equity should also be tracked as a commitment rather than silently treated as a completed grant.

For eligible non-reporting companies, the SEC’s Rule 701 overview describes an exemption for certain compensatory securities sales to employees, consultants, and advisers and additional disclosures when sales exceed $10 million in a 12-month period. Cap-table arithmetic does not establish legal compliance, so confirm the applicable exemption, plan documents, approvals, and disclosures with qualified legal advisers.

Size the pool from the hiring plan

Work backward from the people the company expects to recruit before its next credible financing window. Carta’s option-pool guidance recommends starting with planned grants for individual hires and refresh grants through the next round, then comparing that bottom-up result with relevant benchmarks; it also explains that a pre-money increase lowers the financing price without diluting the incoming investor.

Create one row per planned role, with columns for expected hiring date, level, location, proposed grant, scenario probability, and whether the grant is expressed as shares or a fully diluted percentage. Add identified refresh grants and adviser commitments, followed by a limited contingency for offer negotiation or hiring timing.

For example, a hypothetical plan could reserve 1.2% for a product leader, 0.8% for an engineering lead, 1.4% across four engineers, 0.8% for a sales leader, 0.6% across three go-to-market hires, 0.7% for refresh grants, and 0.5% as contingency. The total is 6%, but it is a planning result rather than a universal benchmark.

If grants are modeled as post-money percentages, their total can supply T in the formula. If the compensation plan uses share counts, total the required shares, subtract usable capacity, and model the resulting ownership directly. Do not combine percentages calculated from today’s capitalization with percentages calculated from the expanded post-money denominator.

What to resolve before signing

Confirm whether the target covers the total plan or only its unallocated portion, whether it is measured before or after the financing, and which securities enter the fully diluted denominator. Model notes, SAFEs, warrants, promised grants, and option exercises according to the transaction documents.

Present three cap-table cases: financing with no top-up, the investor-requested reserve, and the bottom-up hiring requirement. Show every holder’s ownership before the pool increase, after the increase, and after the financing, together with the price per share in each case.

The goal is not simply to minimize the pool. An undersized reserve can constrain planned hiring, while unused excess capacity dilutes existing holders before it supports an operating need. The defensible target is the smallest reserve that covers a documented hiring plan under clearly stated cap-table assumptions.

Also read:

• How to Read a Startup Term Sheet Before You Sign It
• How to Validate a Startup Idea Before You Build the Product
• The SaaS Rule of 40: Choose the Right Growth and Profit Inputs Before You Trust the Score