What percentage of revenue do my top 1, 5, and 10 customers represent?
Your top customers are your best revenue source and your biggest risk. Knowing the exact percentages tells you how fragile your business really is. Here's how to calculate it.
The short answer
Pull your Sales by Customer report, sort by revenue, and divide each tier's total by your overall revenue. If your #1 customer is over 25% of revenue, that's a dependency. If your top 5 are over 60%, your business lives or dies on a handful of relationships. This takes about 10 minutes in QuickBooks, 15 in Xero.
Why the top customer percentage reveals hidden fragility
You have a $600K business. Your top client represents $180K of that, or 30%. They're a great client. They pay on time, they're easy to work with, and they keep growing. Everything feels stable.
Then their new VP of Operations decides to consolidate vendors. They're gone. In one conversation, you lost 30% of your revenue. Your cost structure, your team size, your office lease were all built for $600K. Now you're at $420K with the same overhead.
This scenario plays out constantly in small businesses. The specific percentages tell you exactly how exposed you are and give you time to diversify before the concentration becomes a crisis.
The three concentration tiers every business should track
Concentration risk is best understood at three levels:
These tiers answer different questions. The top-1 percentage is about single-point-of-failure risk. The top-5 is about relationship dependency. The top-10 tells you whether you have a broad base or a narrow one.
How to calculate top customer percentages in QuickBooks Online
- 1Go to Reports → Sales by Customer Summary
Set the date range to the trailing 12 months for a stable picture, or the current quarter for a recent snapshot. Click Run report.
- 2Sort by Total descending
Click the Total column header. Your highest-revenue customers are now at the top. Note the grand total at the bottom.
- 3Calculate each tier
Divide your #1 customer's revenue by the grand total. Then sum your top 5 customers and divide by the grand total. Then sum your top 10. Three quick calculations give you your full concentration profile.
Total time: about 10 minutes. The Sales by Customer Summary report does the heavy lifting. You just need to sort and do three divisions.
How to calculate top customer percentages in Xero
- 1Go to Business → Invoices
Filter by the trailing 12 months. Export the full invoice list to CSV.
- 2Create a pivot table by customer
In your spreadsheet, create a pivot table with customer name as the row and invoice total as the value. Sort descending.
- 3Calculate the three tiers
Same approach: top 1, top 5, top 10 as a percentage of total invoiced revenue.
Total time: about 15 minutes. The pivot table step adds a few minutes over QuickBooks since Xero does not have a built-in Sales by Customer Summary.
What it takes to track these percentages over time
- 10-15 minutes monthly. Quick to pull, but easy to forget. The value is in the trend, not any single snapshot.
- The number lacks forward-looking context. Your top customer might be 20% of revenue, which feels fine. But if they have not placed an order in 45 days and their CRM status shows no upcoming deals, the real risk is higher than the percentage suggests.
- Percentages shift with seasonal patterns. A customer who is 15% of revenue in Q1 might be 30% in Q3 due to seasonal buying. Trailing 12-month windows smooth this out, but quarterly snapshots can be misleading.
Or see your concentration breakdown automatically
Bottomline calculates your top 1, top 5, and top 10 customer concentration percentages every month, rates each tier, and tracks the trend over time. You see the number and the direction.
The trend is the story. A single concentration snapshot is useful. Six months of snapshots showing diversification (or increasing dependency) tells you whether your deliberate efforts to broaden your base are actually working.