OnSumoTools

Series A Dilution Calculator

Model founder ownership before and after a Series A, including option pool shuffle and investor stake, with a sensitivity table on pool size.

100% client-side. Cap table inputs stay in your browser (ons-series-a-dilution-inputs).

Models the standard option pool shuffle: pool expansion dilutes founders before Series A price and ownership are set.

Post-raise founder ownership

57.0%

Down from 70.0% pre-raise (13.0% points of dilution).

Option pool shuffle added 227,273 shares before Series A priced.

Post-money valuation

$12,000,000

Price per share

$0.98

Series A ownership

16.7%

Founder dilution

13.0%

Before Series A
HolderShares%
Founders7,000,00070.0%
Seed investors2,000,00020.0%
Option pool1,000,00010.0%
Series A investors00.0%
Total10,000,000100.0%
After Series A
HolderShares%
Founders7,000,00057.0%
Seed investors2,000,00016.3%
Option pool1,227,27310.0%
Series A investors2,045,40816.7%
Total12,272,681100.0%

Ownership through the round

Pre-raise, after the option pool shuffle, and post-close cap table mix.

After pool shuffle, founders held 68.4% before Series A shares were issued.

Option pool sensitivity

Post-close pool size vs founder and Series A ownership.

Post-close pool %Founder % postSeries A % post
5%58.3%16.7%
7.5%58.3%16.7%
10%(your input)57.0%16.7%
12.5%55.1%16.7%
15%53.1%16.7%

Cap table (pre-raise)

Series A terms

How does the Series A Dilution Calculator work step by step?

When a startup raises a Series A, new shares are created and sold to investors. This increases the total share count, which reduces (dilutes) the percentage ownership of every existing shareholder. The calculator starts with your pre-money valuation and investment amount. Pre-money valuation divided by existing shares gives the price per share. Investment divided by price per share gives the number of new shares issued to investors. The total share count increases, and each existing holder's percentage drops accordingly. The option pool adds another layer: it dilutes founders further because the pool comes from the founders' side, not the investors' side.

What does a typical Series A Dilution Calculator result look like?

Scenario: Two co-founders own 100% of 10,000,000 shares (5,000,000 each). They are raising a $4,000,000 Series A at a $16,000,000 pre-money valuation. The term sheet requires a 15% post-money option pool. Post-money valuation: $20,000,000. Option pool shares: 2,307,692. New investor shares: 3,076,923. Cap table: Founder A from 50% to 32.5% (17.5% dilution). Founder B from 50% to 32.5% (17.5% dilution). Investor gets 20%. Option pool is 15%.

Frequently asked questions

  • What is dilution?

    When a company issues new shares to investors, existing shareholders own a smaller percentage of the total. A founder who owns 70% pre-raise might own 50% after a round that creates 25% new shares on a post-money basis. The dollar value of their stake may still increase. Whether dilution is favorable depends on whether the new capital raises the company's valuation enough to offset the reduced ownership percentage.

  • Why does the option pool come out of the pre-money?

    This is standard VC practice. Investors want the option pool to exist before their shares are priced, so the dilution from the pool falls on founders, not investors. If the pool came out of post-money, investors would share in that dilution, which they typically negotiate to avoid.

  • What is a typical Series A option pool?

    10% to 20% of post-money is standard, with 15% being the most common target. The size depends on how many hires you plan before the next round. Investors will push for a larger pool to avoid future dilution rounds. Founders should negotiate based on a specific hiring plan. Use this metric consistently over time to track improvement rather than optimizing for a single period's snapshot.

  • Does dilution mean I lose money?

    Not necessarily. Dilution reduces your percentage but at a higher valuation, your shares may be worth more. If you own 50% of a $10M company ($5M value) and dilute to 35% of a $20M company ($7M value), your position increased by $2M despite lower percentage ownership.

  • What about anti-dilution provisions?

    Anti-dilution clauses protect investors if the company raises a future round at a lower valuation (a 'down round'). The most common type, weighted average anti-dilution, gives investors extra shares to partially compensate. This calculator does not model anti-dilution adjustments. Those are handled in a full cap table management tool.

  • What about convertible notes and SAFEs?

    If you raised a seed round using convertible notes or SAFEs, those instruments convert to equity at the Series A. You need to calculate the conversion shares first (based on the cap and discount in your note/SAFE), add them to your existing share count, then run the Series A dilution calculation.

Related tools

The pool shuffle most founders miss

Term sheets often say the option pool must be 10 or 15 percent after the round. Sounds neutral. It isn't. The pool is usually created before the money comes in, so it counts against the pre-money valuation.

In plain terms, the new investors don't share that dilution. You and your existing holders carry all of it. A 10 million dollar pre-money with a 15 percent post-close pool is worth less to you than it looks.

Pre and post cap tables

The calculator builds both tables. The pre-close table shows who owns what today. The post-close table adds the new pool and the new shares sold. Compare the founder rows and you'll see exactly how much you give up.

The waterfall chart breaks founder dilution into steps: the pool, then the new money. It's the clearest way to see which term costs you more.

How big should the pool be

Typical Series A pools sit around 10 to 15 percent, sized to cover hires for the next 12 to 24 months. Ask for a hiring plan to back it up. An oversized pool is a quiet price cut.

The sensitivity view shows founder ownership at several pool sizes after closing. Use it when you negotiate. Moving from 15 to 10 percent can be worth more than a small bump in valuation.

Dilution isn't a loss

Owning 70 percent of a company worth 10 million beats owning 100 percent of one worth 2 million. If the money grows the business, a smaller slice of a bigger pie is a good trade.

Still, watch the stack. Seed, Series A, B and employee pools all take a bite.

What the tool leaves out

Anti-dilution clauses, liquidation preferences, and convertible notes or SAFEs convert in ways that change the math. Model those with your lawyer. This tool is a planning aid, not legal or financial advice. Your numbers stay in your browser.