There are many reasons insiders sell: diversification, taxes, divorce, buying a house. There's really only one reason insiders buy: they think the stock is going up.
Open-market insider purchases (Form 4 Code P) are the highest-signal transactions in public markets. Here's how to find the ones that matter.
Why insider buying is different from insider selling
| Action | Reasons | Signal quality |
|---|---|---|
| Insider buying | Believes stock is undervalued | High — one clear reason |
| Insider selling | Diversification, taxes, home purchase, divorce, estate planning, 10b5-1 plans, option expiration | Low — many possible reasons |
When a CEO takes money out of their bank account and buys shares at market price, they're making a concentrated bet with their own wealth. That's as close to a direct conviction signal as public markets offer.
The five characteristics of meaningful insider buys
1. Large relative to compensation
A CEO earning $1M/year buying $50K in stock is a token gesture. A CEO buying $2M — two years of salary — is putting real skin in the game.
Rule of thumb: Look for purchases exceeding 25% of the insider's annual compensation.
2. Open-market, not option exercise
Only Code P (open-market purchase) counts. Code M (option exercise) is compensation mechanics. The insider didn't choose to buy at market price — they exercised a pre-granted option.
How to check: Form 4, Table I, Transaction Code column. P = signal. M = noise.
3. Cluster buying (multiple insiders)
One insider buying could be personal. Three insiders buying in the same week is a consensus view from people who see the company's financials.
The cluster hierarchy:
- CEO alone: moderate signal
- CEO + CFO: strong signal (the two people who know the numbers best)
- CEO + CFO + 2 directors: very strong signal
- 5+ insiders in one week: rare and extremely bullish
4. Buying after a decline
An insider buying after the stock dropped 30% is telling you: "The market overreacted. I've seen the numbers. This is cheap."
An insider buying at all-time highs is still a signal, but weaker — they might just be optimistic rather than seeing mispricing.
5. First purchase in a long time
An insider who hasn't bought in 3 years suddenly placing a large purchase is a louder signal than someone who buys small amounts every quarter as a routine.
How to filter noise
Ignore these
- Small purchases (<$10K): Token compliance buys
- Automatic investment plan purchases: Pre-scheduled, no timing signal
- Purchases on the same day as option exercises: Often just exercising and holding, not fresh conviction
- Director purchases immediately after joining the board: Often required as part of director compensation agreements
Investigate these
- CEO/CFO purchases >$500K: Material conviction
- Multiple insiders buying within 5 business days: Cluster signal
- Purchases within 2 weeks of earnings: They've seen the numbers
- Purchases after >20% stock decline: Contrarian conviction
- First purchase by an insider who previously only sold: Changed outlook
The practical screening process
Step 1: Filter for Code P only
Remove all Code M, F, G, J transactions. You only want open-market purchases.
Step 2: Set minimum dollar threshold
Filter for purchases >$100K to remove token buys. Adjust higher for large-cap companies.
Step 3: Check the insider's role
CEO and CFO purchases carry more weight than director purchases. Officers see day-to-day operations; directors see quarterly board presentations.
Step 4: Calculate purchase size vs. existing holdings
A $500K purchase by an insider who already holds $50M is a 1% add — mild signal. A $500K purchase by an insider who holds $200K is more than doubling their stake — strong signal.
Step 5: Check timing context
- Recent earnings? (post-blackout buying = they liked what they saw)
- Recent stock decline? (buying the dip = conviction)
- Upcoming catalyst? (new product, M&A, regulatory decision)
What insider buying doesn't tell you
- Timing: Insiders are often early. A CEO buying at $50 doesn't mean $50 is the bottom — the stock might go to $30 before recovering.
- Time horizon: Insiders think in years, not weeks. Their buy signal might take 12-24 months to play out.
- External risks: Insiders know their company well but may not anticipate macro shocks, regulatory changes, or competitive disruptions.
The bottom line
Insider buying is the strongest publicly available conviction signal — but only when properly filtered. Focus on large, open-market purchases by senior executives, especially in clusters and after stock declines. Everything else is noise.
Originally published at 13F Insight
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