Dilution Maths Walkthrough: 5 Worked Examples Every Founder Needs

Dilution maths is the arithmetic that determines how much of your company you own after each funding round — and how much you hand to investors, employees and advisors. Every time new shares are issued, your percentage ownership shrinks, even if the value of your stake grows. Understanding dilution maths is not optional for founders: it shapes negotiating power, long-term wealth, hiring capacity and the terms of every subsequent round. This guide walks through five worked examples covering seed rounds, Series A, convertible notes, SAFEs and multi-round cumulative dilution, with the actual calculations laid out step by step.

What is dilution and how does it work?

Dilution is the reduction in your ownership percentage when new shares are issued. It is a mathematical certainty in any funded startup: investors receive shares in exchange for capital, employees receive shares as compensation, and advisors may receive equity for their contributions. The total number of shares increases, and each existing shareholder’s percentage decreases proportionally.

The critical insight is that dilution does not automatically destroy value. A founder who owns 80% of a company worth USD 1 million has USD 800,000 in equity value. After a funding round that dilutes them to 60%, if the company is now worth USD 3 million, their stake is worth USD 1.8 million — more than double despite the lower percentage. Dilution is only damaging when it is excessive, unplanned or obtained on unfavourable terms.

Founders should track dilution from the first share issuance. The cap table — the register of who owns what — is the source of truth, and every transaction that changes share counts must be recorded. Our cap table guide explains the mechanics in detail.

Example 1: Seed round dilution with priced equity

This is the most straightforward scenario: a founder issues new shares directly to seed investors at a fixed price.

Starting position: Founder owns 1,000,000 shares. No other shareholders. Total shares outstanding: 1,000,000. Founder ownership: 100%.

The deal: An angel investor offers USD 300,000 for equity at a pre-money valuation of USD 1.2 million. The post-money valuation is USD 1.5 million.

Calculation:

1. Price per share = Pre-money valuation / Total existing shares = USD 1,200,000 / 1,000,000 = USD 1.20 per share

2. New shares issued to investor = Investment / Price per share = USD 300,000 / USD 1.20 = 250,000 shares

3. Total shares after round = 1,000,000 + 250,000 = 1,250,000 shares

4. Founder ownership post-money = 1,000,000 / 1,250,000 = 80%

5. Investor ownership = 250,000 / 1,250,000 = 20%

The founder’s ownership has diluted from 100% to 80% — a 20 percentage point dilution. The founder now owns 80% of a company worth USD 1.5 million (USD 1.2 million in equity value), compared to 100% of a company worth USD 1.2 million before the round. The founder’s equity value has increased by USD 200,000 despite the dilution.

This is normal and healthy dilution. The investor’s 20% stake is within the standard range for a seed round, where investors typically take 15–25% of the company. Founders should be cautious when a seed investor demands more than 25%, as it leaves insufficient room for future rounds and employee equity.

Example 2: Series A dilution with option pool

Series A rounds introduce two dilutive elements: the investor’s equity and the employee option pool, which is typically created or expanded at the time of the round.

Starting position after seed: Founder owns 1,000,000 shares (80%). Investor owns 250,000 shares (20%). Total: 1,250,000 shares.

The deal: A VC firm invests USD 2,000,000 at a pre-money valuation of USD 8,000,000. The VC requires a 15% employee option pool to be created pre-money (before the investment). Post-money valuation: USD 10,000,000.

Calculation:

1. Option pool shares (pre-money) = 15% of post-money total. Let total post-money shares = X. Option pool = 0.15X. Existing shares + option pool + new VC shares = X.

Simplified: Pre-money valuation USD 8M / post-money USD 10M = 80% goes to existing holders + pool, 20% to VC.

2. Total post-money shares = USD 10,000,000 / price per share. Price per share = USD 8,000,000 / 1,250,000 = USD 6.40

3. Total post-money shares = USD 10,000,000 / USD 6.40 = 1,562,500 shares

4. New VC shares = USD 2,000,000 / USD 6.40 = 312,500 shares

5. Option pool = 1,562,500 × 15% = 234,375 shares

6. Existing shares (founder + seed investor) = 1,250,000 shares

7. Check: 1,250,000 + 312,500 + 234,375 = 1,796,875… Let me recalculate with the correct dilution math.

Correct approach: The option pool is created pre-money, meaning it dilutes existing shareholders before the VC invests.

Post-money total shares = Pre-money existing shares / (1 – option pool % – VC %) = 1,250,000 / (1 – 0.15 – 0.20) = 1,250,000 / 0.65 = 1,923,077 shares

VC shares = 20% × 1,923,077 = 384,615 shares

Option pool = 15% × 1,923,077 = 288,462 shares

Founder shares = 1,250,000 × (1,250,000 / 1,923,077) = 812,500 shares (proportional)

Final ownership:

Founder: 812,500 / 1,923,077 = 42.2%

Seed investor: 250,000 / 1,923,077 × (adjusted proportionally) = 13.0%

VC: 384,615 / 1,923,077 = 20.0%

Option pool: 288,462 / 1,923,077 = 15.0%

The founder’s ownership has dropped from 80% to approximately 42% — a significant dilution driven by both the VC investment and the option pool. This is why founders must model the option pool impact before agreeing to terms. The option pool is “pre-money” in the sense that it comes out of the founder’s and existing investors’ ownership, not the new investor’s. Per our pre-seed funding guide, understanding this dynamic is critical at every stage.

Example 3: Convertible note dilution

Convertible notes are debt instruments that convert into equity at a future priced round. The dilution depends on the valuation cap, the discount rate and the round valuation.

Starting position: Founder owns 1,000,000 shares (100%).

The deal: An angel invests USD 100,000 via a convertible note with a USD 2,000,000 valuation cap and a 20% discount to the next round price. Six months later, the Series A closes at a USD 5,000,000 pre-money valuation, issuing shares at USD 5.00 per share (assuming 1,000,000 pre-money shares).

Calculation:

1. Discounted price = Series A price × (1 – discount) = USD 5.00 × 0.80 = USD 4.00 per share

2. Cap price = Cap valuation / Pre-money shares = USD 2,000,000 / 1,000,000 = USD 2.00 per share

3. Conversion price = lower of discounted price and cap price = USD 2.00 per share

4. Shares issued to note holder = USD 100,000 / USD 2.00 = 50,000 shares

5. Total shares post-conversion = 1,000,000 + 50,000 = 1,050,000 shares

6. Note holder ownership = 50,000 / 1,050,000 = 4.76%

The note holder receives approximately 4.76% of the company for USD 100,000 — a favourable outcome driven by the low valuation cap. The founder dilutes from 100% to approximately 95.2% from the note alone. However, the Series A investor then receives their own equity on top of this, further diluting the founder. The key lesson: convertible notes are not “future dilution-free” — they convert and dilute, and the cap and discount determine how much. Our SAFE vs convertible note comparison explores the differences in detail.

Example 4: SAFE dilution with valuation cap

SAFEs (Simple Agreements for Future Equity) function similarly to convertible notes but are not debt instruments. The dilution maths follow the same logic.

Starting position: Founder owns 1,000,000 shares (100%).

The deal: An angel invests USD 50,000 via a post-money SAFE with a USD 3,000,000 valuation cap and no discount. The SAFE specifies that the cap determines the conversion price.

Calculation:

1. SAFE conversion shares = Investment / (Cap valuation / Pre-money shares) = USD 50,000 / (USD 3,000,000 / 1,000,000) = USD 50,000 / USD 3.00 = 16,667 shares

2. Total shares post-conversion = 1,000,000 + 16,667 = 1,016,667 shares

3. SAFE holder ownership = 16,667 / 1,016,667 = 1.64%

4. Founder ownership = 1,000,000 / 1,016,667 = 98.36%

The SAFE dilutes the founder by approximately 1.64 percentage points. This is modest because the SAFE amount is small relative to the cap. However, if the SAFE were USD 500,000, the dilution would be proportionally larger — approximately 14.3%. The valuation cap is the critical variable: a lower cap creates more dilution for the same investment amount. Founders should model every SAFE conversion before raising the next priced round to understand the cumulative dilution effect. Per our pre-seed pitch deck guide, showing investors a clean cap table with all conversions modelled builds credibility.

Example 5: Multi-round cumulative dilution

The most important dilution maths exercise is tracking cumulative dilution across multiple rounds. Founders who focus only on the current round miss the cumulative effect.

Scenario: A founder starts with 1,000,000 shares and goes through four rounds:

Calculation detail for pre-seed: Price per share = USD 500,000 / 1,000,000 = USD 0.50. New shares = USD 100,000 / USD 0.50 = 200,000. Total = 1,200,000. Founder = 1,000,000 / 1,200,000 = 83.3%.

Seed: Price per share = USD 1,200,000 / 1,200,000 = USD 1.00. New shares = USD 300,000 / USD 1.00 = 300,000. Total = 1,500,000. Founder = 1,000,000 / 1,500,000 = 66.7%.

Series A: Price per share = USD 8,000,000 / 1,500,000 = USD 5.33. New shares = USD 2,000,000 / USD 5.33 = 375,188. Total = 1,875,188. Founder = 1,000,000 / 1,875,188 = 53.3%.

Series B: Price per share = USD 32,000,000 / 1,875,188 = USD 17.07. New shares = USD 8,000,000 / USD 17.07 = 468,659. Total = 2,343,847. Founder = 1,000,000 / 2,343,847 = 42.7%.

The founder retains 42.7% after raising a total of USD 10.4 million. This is within the acceptable range for a founder who has raised through Series B — most Series B-backed founders own between 30–50%, per standard cap table benchmarks. The founder’s stake, while diluted, represents a significant equity value: 42.7% of a company valued at USD 40 million (post-money Series B) is worth approximately USD 17.1 million. Our venture studio equity guide provides context on how these dynamics shift in studio models.

“Founders who do not model dilution before every round are negotiating blind. The maths is not complicated — it is arithmetic — but the consequences of getting it wrong compound across every subsequent round. A founder who gives away 5% too much at seed does not lose 5% at Series A; they lose 5% of their remaining stake, and the effect ripples forward indefinitely.”

— Mustafa Hasan, Founding Partner, Valu.vc

What are the most common dilution maths mistakes?

Founders make five recurring errors when calculating or negotiating dilution.

Ignoring the option pool. The pre-money option pool is the most common surprise for founders. The pool dilutes existing shareholders, not the new investor, and a 15–20% pool at Series A can reduce founder ownership by 10–15 percentage points more than the investor’s stake alone. Always model the pool impact separately from the investor’s equity.

Confusing pre-money and post-money valuation. The difference matters. A USD 5 million pre-money valuation with a USD 1 million investment creates a USD 6 million post-money valuation and 16.7% dilution. A USD 5 million post-money valuation with the same investment means only USD 4 million pre-money and 20% dilution. Always clarify which number the investor is quoting.

ForgettingSAFE and note conversions. Existing SAFEs and convertible notes convert at the next priced round, increasing the total share count before the new investor’s percentage is calculated. Founders who model only the new investment, without accounting for conversions, underestimate the dilution they will experience.

Not modelling employee equity. Employee grants reduce the available equity pool and dilute founders. A company that issues 10% of its equity to employees over time dilutes founders proportionally. Founders should track projected employee grants alongside investor dilution.

Focusing on percentage instead of value. A founder who retains 60% of a company worth USD 10 million (USD 6 million) is better off than one who retains 80% of a company worth USD 3 million (USD 2.4 million). Dilution maths must be evaluated in the context of company value, not in isolation.

For founders navigating these calculations, our runway maths framework integrates dilution modelling with burn rate and funding timeline planning.

Frequently asked questions about dilution maths

What is dilution in startup equity?

Dilution is the reduction in a founder’s or existing shareholder’s ownership percentage when new shares are issued to investors. It occurs at every funding round because the company creates new shares to sell to investors, increasing the total share count. Dilution does not necessarily reduce the value of your stake — if the company grows, a smaller percentage of a larger company can be worth more.

How do you calculate dilution after a funding round?

Divide the new shares issued by the total shares after the round to find the investor’s percentage. Then subtract that from 100% to find the founder’s remaining stake. For example, if a founder owns 1,000,000 shares and issues 250,000 new shares to investors, the founder owns 1,000,000 / 1,250,000 = 80% post-money.

What is anti-dilution protection?

Anti-dilution clauses protect investors if a subsequent round prices shares lower than they paid. Full ratchet adjusts the investor’s conversion price to the new lower price, while weighted average adjusts it based on the relative size of the new round. Weighted average is more common and less punitive to founders than full ratchet.

How does a SAFE affect founder dilution?

A SAFE converts into equity at the next priced round, typically at a discount to the round price or subject to a valuation cap. The dilution effect depends on the cap, the discount and the round valuation. A high cap means less dilution; a low cap means more. Founders must model the SAFE conversion to understand true post-money ownership before the round closes.

Should a founder worry about dilution?

Moderate dilution is normal and expected — it is the price of capital that grows the company. The concern should be excessive dilution that leaves founders without sufficient ownership to maintain motivation and control. Founders should model dilution before every round, track cumulative ownership and ensure they retain at least 50–60% through Series A unless the growth trajectory justifies more.

Dilution maths is the discipline that protects founder ownership across the lifecycle of a funded startup. The five examples in this walkthrough — seed, Series A, convertible notes, SAFEs and multi-round cumulative dilution — cover the scenarios founders face most frequently. The core principle is simple: model every round before you negotiate, track cumulative dilution, and never sign terms you have not calculated. Founders ready to raise should review our pre-seed pitch deck guide and first 30 investors guide to pair dilution understanding with a strong fundraising strategy.

Apply for pre-seed funding