Equity Dilution Calculator

Equity dilution occurs when a company issues new shares, reducing the ownership percentage of existing shareholders. Every time a startup raises a funding round or expands its employee option pool, the total share count grows — and each existing shareholder's slice of the pie shrinks proportionally. Understanding dilution is critical for founders, early employees, and angel investors who want to track the real value of their stake over time.

Dilution is not inherently bad. If a company raises capital at a higher valuation than the previous round, the new price per share rises and the absolute dollar value of your shares may increase even as your percentage ownership falls. This is the classic trade-off: give up a percentage point of ownership, gain a higher-valued company. The equity dilution calculator lets you model both sides of that trade-off simultaneously.

There are two primary sources of dilution you need to model for any funding round. First, there are the new investor shares — shares issued directly to the incoming investor in exchange for their capital. Second, there is the option pool increase — shares reserved for future employee grants that are typically created at the same time as a funding round, often at the insistence of the lead investor. Both reduce your ownership percentage, so both must be included in any honest dilution analysis.

The equity dilution calculator on this page handles both sources in one calculation, giving you a precise picture of your pre-round ownership, your post-round ownership, the absolute dilution in percentage points, and the relative dilution as a fraction of your original stake. It also computes the post-money valuation and the implied price per share, so you can compare how the dollar value of your position changes even as the percentage shrinks.

The calculator uses the following sequence of formulas. Every variable corresponds directly to an input field on this page.

Core Dilution Math

Start with your pre-round ownership percentage:

Pre-Ownership % = (Your Shares ÷ Current Total Shares) × 100

Next, compute the total new shares created by the round (investor shares plus any option pool expansion):

Total New Shares = New Investor Shares + Option Pool Increase

Then calculate the new post-round total shares:

Post-Round Shares = Current Total Shares + Total New Shares

Your post-round ownership uses your unchanged share count divided by the larger post-round total:

Post-Ownership % = (Your Shares ÷ Post-Round Shares) × 100

The absolute dilution (in percentage points) and relative dilution (as a fraction of your original stake) follow naturally:

Absolute Dilution = Pre-Ownership % − Post-Ownership %

Relative Dilution % = (Absolute Dilution ÷ Pre-Ownership %) × 100

Valuation and Share Price

The post-money valuation is simply the pre-money valuation plus the investment amount:

Post-Money Valuation = Pre-Money Valuation + Investment Amount

The price per share implied by the round divides the post-money valuation by the post-round share count:

Price Per Share = Post-Money Valuation ÷ Post-Round Shares

Your pre-round share value uses the pre-money price per share:

Pre-Round Value = Your Shares × (Pre-Money Valuation ÷ Current Total Shares)

Your post-round share value uses the new price per share:

Post-Round Value = Your Shares × Price Per Share

Once you enter your cap table data, the calculator displays several key metrics. Here is what each one means and how to use it when evaluating a funding round.

Pre-Round Ownership % is your baseline — the percentage of the company you own before any new shares are issued. It is calculated from your current shares and the current total share count.

Post-Round Ownership % is the critical number. This is your ownership stake after both the investor shares and any option pool expansion are added to the cap table. Because your own share count does not change, your percentage falls as the denominator grows.

Absolute Dilution tells you how many percentage points you lost. If you owned 10% before and own 7.69% after, the absolute dilution is 2.31 percentage points. This is the number most commonly cited in term sheet negotiations.

Relative Dilution expresses the same loss as a fraction of your original ownership. Losing 2.31 points from a 10% stake is a 23.1% reduction in your proportional ownership. This metric is useful when comparing dilution across shareholders with very different starting stakes.

Price Per Share and Value Change are the economic counterbalance to dilution. Even if you lose percentage points, a higher implied price per share may increase the total dollar value of your position. When the post-round value exceeds the pre-round value, you are experiencing dilution with appreciation — the common outcome in up-rounds. When it falls, you may be in a down-round scenario worth examining carefully.

The Post-Round Cap Table summary at the bottom of the results panel breaks down investor ownership percentage and option pool percentage separately, so you can see exactly who owns what after the dust settles.

One of the most consequential — and least understood — aspects of startup dilution is the option pool shuffle. Investors often require a company to expand its unallocated employee option pool before the round closes, using pre-money shares. This means the option pool increase is counted in the pre-money valuation, not the post-money valuation, which effectively lowers the price per share paid by the investor while increasing dilution borne entirely by existing shareholders.

This calculator models the option pool increase as new shares added to the post-round total, which is the standard economic treatment. In practice, term sheets may structure this differently, so always read the pre-money/post-money option pool language in your term sheet carefully. The key question is: are the new option pool shares counted before or after the investor's price per share is set?

When you enter an option pool increase in this calculator, those shares increase the post-round total share count, which lowers both your ownership percentage and the implied price per share. Investors benefit from a larger option pool because it keeps the company's future hiring costs funded without diluting the post-round cap table — but existing shareholders bear the cost upfront.

A common rule of thumb is that a healthy option pool for an early-stage company ranges from 10% to 20% of the post-round fully diluted share count. If your investor is requesting a pool refresh that pushes well beyond that range, it is worth negotiating the size down or requesting that a portion be allocated post-money instead of pre-money.

Not all dilution is created equal. When a company raises money at a lower valuation than a prior round — a down round — the impact on existing preferred shareholders can be amplified by anti-dilution provisions embedded in prior investment agreements. Understanding these provisions is essential for founders and common shareholders who want to predict their actual post-round ownership.

The two most common anti-dilution mechanisms are full ratchet and weighted average. Full ratchet is the harshest: it reprices prior investors' shares to the new lower price per share, potentially issuing them many additional shares and dramatically diluting everyone else. Weighted average (both broad-based and narrow-based variants) is more moderate: it adjusts the prior investors' conversion price based on a formula that accounts for both the new price and the number of new shares issued.

This equity dilution calculator models straightforward new-round dilution without anti-dilution adjustments. If you are in a down-round scenario or have preferred shareholders with full-ratchet provisions, the actual dilution you experience may be significantly greater than what this calculator shows. In those situations, work with a startup attorney or financial advisor to model the full cap table impact.

For typical up-rounds — the scenario most seed and Series A founders face — this calculator gives you an accurate, fast estimate of where everyone stands after the round closes. Use it to model multiple scenarios: what if the investor wants 20% instead of 19%? What if the option pool refresh is 100,000 shares instead of 50,000? Iterating through scenarios quickly is where the equity dilution calculator saves you real time in term sheet negotiations.