PORTLENS BLOG
What Is ETF Overlap? How to Check It and How Much Is Too Much
ETF overlap is the share of two funds' portfolios invested in the same stocks. Here's how overlap is measured, real numbers for popular pairs, and when it actually hurts.
How to Calculate Portfolio Beta (With a Worked Example)
Portfolio beta is the weighted average of your holdings' betas. Here's the formula, a worked example, what counts as a benchmark, and the edge cases that make naive beta calculations wrong.
Diversification Beyond Sector Splits: Factors, Geography, and Correlation Regimes
Sector diversification is table stakes — and often an illusion. Real diversification spreads factor exposures, geographies, and holds up when correlations spike. Here's a practical checklist.
The Minimum Variance Frontier, Explained Simply
The minimum variance frontier is the set of portfolios with the lowest possible risk for each level of expected return. Here's the intuition, why most portfolios sit far from it, and its real-world limits.
Factor Exposure: The Risk Your Sector Breakdown Hides
Factors — market, size, value — explain why stocks move together across sector lines. Here's how factor exposure is measured with a Fama-French regression and why sector-diversified portfolios can still be one concentrated bet.
What Is Real Diversification? (It's Not the Number of Stocks You Own)
Real diversification means holding assets that don't move together. Here's why 30 correlated stocks aren't diversified, how effective holdings are measured, and how to check your own portfolio.