ETF Overlap Checker
Estimate how much overlap exists between two ETFs in your portfolio. Enter tickers, weights, expense ratios, and an overlap percentage to see duplicate exposure, unique exposure, and the blended fee you pay on the combined position.
ETF overlap and blended fee formulas
When you hold multiple ETFs, it’s easy to assume you are diversifying. In reality, many broad funds share a large portion of their holdings. The ETF overlap checker uses simple formulas to estimate duplicate exposure, unique exposure, and the blended expense ratio on your combined ETF allocation.
1. Portfolio weights and dollar exposure
Portfolio value:
V
ETF A weight (decimal):
w_A = Weight A (%) ÷ 100
ETF B weight (decimal):
w_B = Weight B (%) ÷ 100
Dollar exposure:
Exposure_A = V × w_A
Exposure_B = V × w_B
These formulas convert your percentage weights into dollar amounts invested in each ETF.
2. Overlap percentage and duplicate exposure
Estimated overlap (decimal):
o = Overlap (%) ÷ 100
Duplicate exposure (approximate):
Duplicate ≈ o × min(Exposure_A, Exposure_B)
The checker uses the smaller of the two ETF exposures as the base for overlap, then applies your overlap percentage to estimate how much of your portfolio is invested in the same holdings through both funds.
3. Unique exposure
Total ETF exposure:
Total_ETF = Exposure_A + Exposure_B
Unique exposure:
Unique = Total_ETF − Duplicate
Unique exposure represents the portion of your ETF allocation that is not duplicated across the two funds.
4. Blended expense ratio
Expense ratios (decimal):
e_A = Expense A (%) ÷ 100
e_B = Expense B (%) ÷ 100
Blended expense ratio:
e_blend = (w_A × e_A + w_B × e_B) ÷ (w_A + w_B)
This weighted average shows the effective fee you pay on the combined ETF position, based on each fund’s share of the allocation.
5. Scenario schedule
For N steps, overlap levels:
o_k = k × (100 ÷ N)%, for k = 0 … N
For each o_k:
Compute Duplicate_k and Unique_k using the formulas above.
The schedule lets you see how duplicate and unique exposure change as overlap increases from 0% to 100%, helping you understand the trade-offs between diversification and concentration.
Why ETF overlap matters for diversification and fees
Owning multiple ETFs can feel like a sophisticated strategy, but without checking overlap you may simply be stacking the same holdings on top of each other. Overlap affects both diversification and fees: you might be paying multiple managers to hold the same stocks, while concentrating risk in a narrow slice of the market. The ETF overlap checker is designed to make this invisible structure visible.
Understanding overlap in practice
Many popular ETFs track broad indexes such as the total U.S. market, the S&P 500, or large-cap growth. These indexes share a core set of mega-cap companies. If you own a total market ETF and a large-cap ETF, the top holdings may be nearly identical. That means a large portion of your portfolio is effectively invested in the same names twice. Overlap is not inherently bad, but it changes the risk profile of your portfolio and can reduce the benefit of adding more funds.
How the checker models your situation
To use the tool, you enter the tickers for ETF A and ETF B, their weights in your portfolio, and each fund’s expense ratio. You then estimate the overlap percentage based on holdings data from fact sheets or research tools. The checker converts your weights into dollar exposures, applies the overlap percentage to the smaller exposure, and calculates duplicate and unique exposure. It also computes a blended expense ratio, showing the effective fee you pay on the combined ETF allocation.
Worked example
Imagine a $100,000 portfolio where ETF A (a total market fund) is 60% and ETF B (a large-cap fund) is 40%. ETF A charges 0.03% and ETF B charges 0.09%. You estimate that 70% of the large-cap fund’s holdings overlap with the total market fund’s top positions. You enter:
- ETF A weight: 60%
- ETF B weight: 40%
- Overlap: 70%
- Portfolio value: $100,000
The checker shows that ETF A represents $60,000 and ETF B represents $40,000. The smaller exposure is $40,000, and 70% of that—$28,000—is estimated duplicate exposure. The remaining $72,000 is unique exposure across both funds. The blended expense ratio is a weighted average of 0.03% and 0.09%, reflecting the combined fee on the $100,000 ETF allocation.
Using the scenario schedule
The scenario schedule varies the overlap percentage from 0% to 100% in steps you choose (for example, 10 steps). For each level, it calculates duplicate and unique exposure. This helps you see how quickly duplicate exposure grows as overlap increases. At 0% overlap, all exposure is unique; at 100% overlap, the smaller ETF is entirely duplicated by the larger one. Exporting the schedule to CSV lets you build charts or compare different ETF pairs.
Practical tips
- Use fund provider tools and independent research sites to get more precise overlap estimates.
- Be cautious about owning multiple broad market funds that track similar indexes; overlap is often high.
- Consider whether each ETF adds truly distinct exposure (such as different regions, factors, or sectors) rather than duplicating what you already own.
- Remember that fees compound over time—if you are paying multiple funds to hold the same stocks, you may be able to simplify and reduce costs.
Frequently Asked Questions
Does the checker use actual holdings data?
No. It uses your estimated overlap percentage and simple weighting formulas. For precise overlap, you would need full holdings data from each ETF.
What if my weights don’t add up to 100%?
The tool focuses on the combined ETF allocation. Your weights can sum to less than or more than 100% of your total portfolio; the calculations are based on the percentages you enter.
Can I use the tool with more than two ETFs?
This version is designed for two ETFs at a time. You can run multiple comparisons to understand overlap across different pairs.
How should I choose the overlap percentage?
Start with a rough estimate based on top holdings lists or third-party overlap tools. Then test a range of overlap levels using the scenario schedule.
Is this financial advice?
No. This tool is for education and planning. It helps you visualize overlap and fees, but it is not personalized financial advice.
Can I export the overlap scenarios?
Yes. Use the Export CSV button to download the scenario table and analyze it in a spreadsheet.
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Information on this site is for educational purposes only and is not financial, tax, or legal advice. Calculations are estimates and may not reflect actual results. See our Privacy Policy and Disclaimer.