67% of founders miscalculate dilution at exit—thinking they own 35% when reality is 22%. Option pool timing, SAFE conversions, and Series B anti-dilution clauses hide 13 percentage points. This step-by-step models your exact ownership through pre-seed SAFEs → Seed → Series A/B/C with Google Sheets formulas, real cap table from $100K → $100M raise showing 10% founder stake becoming 3.2%, and the “gross-up trap” that costs 4% extra per round.
Table of Contents
- Dilution Basics and Formulas
- SAFE Conversion Mechanics
- Option Pool Gross-Up Trap
- Round-by-Round Walkthrough
- Anti-Dilution Impact Modeling
- Exit Scenarios by Ownership
- Common Mistakes Founders Make
- Frequently Asked Questions About Dilution Modeling
Dilution Basics and Formulas
Core Formula:
Your New Ownership % = Your Shares / Total Shares After Round × 100Total Shares After Round:
= Previous Shares + New Investor Shares + Option Pool Increase + SAFE ConversionsDilution Per Round (Typical):
| Round | Amount | Dilution | Founder % After |
|---|---|---|---|
| Pre-Seed SAFE | $250K | 0% (converts later) | 100% |
| Seed | $2M at $8M pre | 20% | 80% |
| Series A | $8M at $32M pre | 20% | 64% |
| Series B | $20M at $80M pre | 20% | 51.2% |
| Series C | $40M at $160M pre | 20% | 41% |
Reality Check: Starting at 100% → 41% after 4 rounds raising $70M total.
Before building your model, Fundreef’s calculator simulates 50 dilution paths with your exact round sizes—spotting the gross-up trap instantly.
SAFE Conversion Mechanics
Post-Money SAFE Math:
SAFE Shares = Investment Amount / (Valuation Cap / Fully Diluted Shares at Conversion)Example:
- $500K SAFE at $5M cap
- Seed round: $2M at $10M post ($1/share)
- Fully diluted shares: 10M
- SAFE converts: $500K ÷ ($5M / 10M shares) = $500K ÷ $0.50 = 1M shares
- SAFE investor gets: 1M / 11M = 9.1% (not 5%!)
Key Trap: SAFE dilutes everyone at conversion, not when you signed it. Model this before raising.
Multiple SAFEs:
Total SAFE Dilution = SUM(Each SAFE Investment / Conversion Price)3 SAFEs ($200K, $300K, $500K) at different caps = complex waterfall.
Option Pool Gross-Up Trap
The Hidden 4% Dilution:
Investor: “We need 15% option pool post-money.”
Wrong (Founder thinking): 15% comes from everyone proportionally.
Right (Reality): 15% pool created pre-investment dilutes only existing shareholders.
Formula:
Pre-Money Pool Increase = Target Post % / (1 - Investment %) - Current Pool %Example (Series A):
- Current pool: 10%
- Target post-raise: 15%
- Investment dilution: 20%
- Required pre-money pool: 15% / (1 – 20%) = 18.75%
- Pool increase needed: 18.75% – 10% = 8.75%
- This 8.75% dilutes founders BEFORE the 20% investment dilution
Effective Dilution:
= Pool Increase + (Investment % × (1 - Pool Increase))
= 8.75% + (20% × 91.25%) = 8.75% + 18.25% = 27%Result: Advertised 20% round = 27% real dilution to founders.
Negotiate pool timing aggressively. Post-money pools save 3-5% per round.
Round-by-Round Walkthrough
Starting Point: 2 Co-Founders
- Total shares: 10,000,000
- Each founder: 5,000,000 (50%)
- Valuation: $0
Pre-Seed: $250K SAFE at $3M Cap
- No dilution yet (converts at Seed)
- Founders still: 50% / 50%
Seed: $2M at $8M Pre + 15% Pool
- Pre-money shares: 10M
- Pool gross-up: 15% / (1 – 20%) = 18.75% post, so add 2.08M shares pre-investment
- New total pre-investment: 12.08M
- SAFE converts: $250K at $3M cap = 1M shares
- New total: 13.08M
- Investor shares (20%): 3.27M
- Final shares: 16.35M
Ownership Post-Seed:
| Holder | Shares | % |
|---|---|---|
| Founder 1 | 4.14M | 25.3% |
| Founder 2 | 4.14M | 25.3% |
| SAFE | 1M | 6.1% |
| Seed VC | 3.27M | 20% |
| Option Pool | 2.45M | 15% |
| Dilution from 50% → 25.3% per founder |
Series A: $8M at $32M Pre + 10% Pool Top-Up
- Current pool: 15% (2.45M of 16.35M)
- Target: 20% post-raise
- New VC wants 20%
- Pool gross-up: (20% / (1-20%)) – 15% = 10% increase
- Add 1.8M shares (dilutes existing 10%)
- New investor: 4.54M shares (20%)
- Final shares: 22.69M
Ownership Post-A:
| Holder | Shares | % | Change |
|---|---|---|---|
| Founder 1 | 3.73M | 16.4% | -8.9pp |
| Founder 2 | 3.73M | 16.4% | -8.9pp |
| SAFE | 900K | 4% | -2.1pp |
| Seed VC | 2.94M | 13% | -7pp |
| Series A | 4.54M | 20% | New |
| Pool | 4.54M | 20% | +5pp |
Use Fundreef’s round-by-round simulator to model your exact scenario with 5-year hiring plan impacting pool size.
Anti-Dilution Impact Modeling
Down Round = Extra Pain
Scenario: Series B at $40M pre (down from $50M Series A post)
Weighted Average Anti-Dilution (Standard):
New Price = ((Old Price × Old Shares) + New Investment) / (Old Shares + New Shares)Series A investors paid $2/share. Series B at $1.50/share triggers adjustment.
Full Ratchet (Toxic):
All Series A shares reprice to $1.50 → doubles Series A ownership, massacres founders.
Math Example:
- Series A: $10M at $2/share = 5M shares (20%)
- Series B: $10M at $1.50/share = 6.67M shares
- Full ratchet: Series A gets 6.67M shares (vs original 5M)
- Extra 1.67M shares = 5.5% extra dilution to founders
Avoid: Never accept full ratchet. Weighted average costs <2% in realistic scenarios.
Exit Scenarios by Ownership
$100M Exit, $50M Raised Total:
| Founder % | 1x Liq Pref | Payout | Net Worth |
|---|---|---|---|
| 50% | $50M to VCs first | $50M | $50M |
| 30% | $50M to VCs | $15M | $15M |
| 15% | $50M to VCs | $7.5M | $7.5M |
| 10% | $50M to VCs | $5M | $5M |
$30M Exit (Below Total Raised):
- VCs: $30M (1x prefs = 100%)
- Founders: $0
Lesson: Keep >25% through Series B or ensure $100M+ exit paths clear.
Common Mistakes Founders Make
1. Ignoring Pool Timing (Costs 4% Per Round)
Always negotiate: “15% pool post-money, not pre.”
2. Forgetting SAFE Dilution
$1M in SAFEs at low caps = 8-12% dilution at Seed, not 0%.
3. Compounding Math Wrong
3 rounds of 20% ≠ 60% dilution. It’s 48.8% (0.8 × 0.8 × 0.8 = 51.2% remaining).
4. Not Modeling Downside
“We’ll raise every 18 months” → Reality: 30 months → emergency bridge → extra 10% gone.
5. Skipping Lawyer Review
$3K legal review catches $300K option pool gross-up tricks.
Google Sheets Template (Copy This):
Column A: Round Name
Column B: Pre-Money Valuation
Column C: Investment Amount
Column D: Post-Money Valuation (=B+C)
Column E: Investment % (=C/D)
Column F: Pool Target %
Column G: Pool Increase (=F/(1-E) - Previous Pool)
Column H: Your New % (=Previous % × (1-G) × (1-E))Before finalizing Series A terms, stress-test 3 scenarios (base/pessimistic/optimistic) with Fundreef’s dilution modeler to avoid surprises.
Frequently Asked Questions About Dilution Modeling
How much dilution is normal per round?
15-25% per round. Seed 20%, Series A 20%, B 20%, C 15%. Cumulative = 51% after Series B.
Do option pools dilute founders or everyone?
Depends on timing. Pre-money pools dilute existing holders only. Post-money dilutes everyone including new investors.
How do SAFEs affect dilution?
They convert at next priced round, adding shares. $500K SAFE at $5M cap = 5-10% dilution depending on priced round terms.
Can I avoid dilution?
No, but optimize: High valuations, small rounds, post-money pools, no anti-dilution, keep ownership >25% through B.
What’s weighted average anti-dilution?
Adjusts investor price partially in down rounds. Formula weights old shares vs new. Costs founders 1-3% vs full ratchet’s 8-15%.
How to model dilution in Google Sheets?
Use formula: New % = Old % × (1 – Pool Increase) × (1 – Investment %). Track across 5 rounds minimum.
