Can you name your expected revenue for each month, from memory, accurately?
The gap between a business's high and low months.
Circle of competence means the numbers, not a general impression.
Test Whether You Actually Know Your Own Cycle
Charlie Munger's published circle-of-competence principle draws a line between what someone genuinely understands and what merely sounds familiar, and circle of competence applied to seasonal business cash flow tests whether an owner actually knows their month-by-month pattern in numbers, or just has a general impression of "slower winters." For example, consider a landscaping business owner who described winter as "a bit slower" without ever calculating the actual gap, only to discover, once the last 24 months of statements were reviewed, that December through February revenue averaged $4,100 a month against a $10,300 average for the rest of the year, a $6,200 monthly gap that had never been sized precisely, let alone reserved against. The Berkshire Hathaway letter archive documents Munger's consistent emphasis on genuine, specific understanding over a general, comfortable impression. As of July 2026, this is especially important if you've described your own seasonal pattern in words like "slower" or "busier" without ever calculating the actual monthly numbers behind them.
A vague impression understated the real size of the winter cash-flow dip.
Replace the Impression With the Numbers
Per Poor Charlie's Almanack, genuine understanding, verified against real data, was treated as fundamentally different from a comfortable, untested assumption. Comparing your reserve's rate against a benchmark like 4.20% APY, confirmed through CFPB business-banking resources, ensures the cash you've calculated and set aside isn't losing value while it waits, and still carries standard FDIC coverage.
| Test | What it reveals | Next check |
|---|---|---|
| Can you name each month's expected revenue from memory? | Genuine understanding versus general impression | Compare your memory against 24 months of actual statements |
| Do you know your exact low-month average? | Whether a specific number exists at all | Calculate it directly from historical data |
| Is your reserve sized to the calculated gap? | Whether preparation matches the real pattern | Adjust reserve size to the actual seasonal dip |
| Has your pattern changed in the last 1-2 years? | Whether an old assumption is now stale | Recalculate periodically as the business evolves |
Calculating your actual seasonal pattern has real benefits: it replaces a comfortable but imprecise impression with a number you can actually plan and reserve against. The risk of relying on a general impression, as the landscaping example shows, is under-preparing for a gap that's larger, or timed differently, than assumed. However, that said, it depends on how much your business has genuinely changed compared to your last calculation: a newer business or one that's shifted its client mix may need to recalculate more often than one with a long, stable history. If you're deciding whether to trust your current impression of your seasonal pattern, choose to trust it if you've calculated it from actual data within the past year; choose to recalculate if you're relying on memory or a general sense alone. This is when this matters most: before the next seasonal dip arrives, not during it.
Pull 24 months of actual revenue data, don't rely on impression.
A dollar figure, not a general sense of 'slower.'
Not a generic buffer disconnected from your actual pattern.
An old assumption can go stale as clients and revenue shift.
When This May Not Apply
A very new business with limited historical data may not yet have enough information to calculate a reliable seasonal pattern, and should build in extra caution until more data accumulates. This is especially important to distinguish from an established business that simply hasn't done the calculation yet.
What to Do Next, in 20 Minutes
- Pull 24 months of actual monthly revenue data, not your general impression of it.
- Calculate your actual peak and low-month averages.
- Compare the calculated gap against your current reserve.
- Read margin of safety for variable and self-employed income and business cash-flow cycles for related frameworks, and best small business checking accounts for account options.
- Run a full Money Map check to see this alongside your full financial picture.
Sources and Methodology
This article applies Charlie Munger's published circle-of-competence principle to seasonal business cash-flow planning. It is educational and does not recommend any specific institution.
- Berkshire Hathaway letters· Checked 2026-07-10
- Poor Charlie's Almanack· Checked 2026-07-10
- Consumer Financial Protection Bureau consumer tools· Checked 2026-07-10
- SwitchWize methodology· Checked 2026-07-10
Next scheduled verification: 2026-10-10
Educational content from the SwitchWize Research Desk. Charlie Munger and related entities are not affiliated with or endorsing SwitchWize.
Connect the lesson
Turn the article into a next step.
Switchwize takeaway
Protect the base first.
Review cash, debt, fees, and product fit before chasing the next financial upgrade.
Map my seasonal cash cycle →Frequently asked questions
What does circle of competence mean for a seasonal business?+
How do I test whether I actually understand my seasonal pattern?+
Why does this matter more than a general reserve target?+
Disclaimer
This article is educational and does not provide personalized investment, tax, legal, or financial advice. Charlie Munger, the Munger estate, Berkshire Hathaway, and related entities are not affiliated with or endorsing SwitchWize. References to public letters, speeches, and books are used for educational interpretation only.