A monthly P&L review lives or dies on what you choose to flag. Flag too much and the client stops reading. Flag too little and the one thing that mattered slips through. The fix is a simple rule with two thresholds, applied to every line. To try thresholds on your own numbers, use the free variance calculator.
Why one threshold isn't enough
Most firms start with one test and quickly run into its blind spot:
- Dollars only ("flag anything over $2,500"): payroll, contractors and rent move by thousands every month on normal fluctuation, so they're flagged every time and the flags lose meaning.
- Percent only ("flag anything over 20%"): bank charges going from $40 to $80 is a 100% increase. It's technically a variance, but nobody cares.
Requiring both solves it. A line is flagged only when the change is large in dollars and unusual for that account.
Choosing the dollar threshold (materiality)
Scale it to the client. A practical starting point is 1–2% of average monthly revenue, rounded to a simple number:
| Monthly revenue | 1% | 2% | Reasonable starting threshold |
|---|---|---|---|
| $40,000 | $400 | $800 | $500 |
| $150,000 | $1,500 | $3,000 | $2,500 |
| $600,000 | $6,000 | $12,000 | $10,000 |
For clients with thin margins, lean toward the low end, because small cost movements have a big effect on profit. For clients with high, stable margins you can go higher.
Choosing the percentage threshold
20% is a sensible default. It's high enough to ignore normal month-to-month wobble and low enough to catch real changes. Go down to 10–15% for accounts that should be very stable, such as rent, insurance or software subscriptions. Go up to 25–30% for accounts that are naturally lumpy, such as repairs, advertising or travel.
The rule in action
With a $2,500 threshold and 20%, here's how September looks for a fictional client, Harbor & Pine Co.:
| Line | MoM $ | MoM % | Over $? | Over %? | Flagged |
|---|---|---|---|---|---|
| Contractors | +$2,700 | +5.8% | Yes | No | No |
| Professional fees | +$6,120 | +196% | Yes | Yes | Yes |
| Materials | +$2,900 | +29.6% | Yes | Yes | Yes |
| Travel | −$1,340 | −45.0% | No | Yes | No |
| Bank charges | +$15 | +5.1% | No | No | No |
| Consulting income (new) | +$3,000 | n/a | Yes | prior was $0 | Yes |
Three flags out of a full P&L, each worth a sentence of explanation. That's the right size for a client report.
Edge cases to handle
Lines that start or end at zero
If last month was $0, the percentage change is undefined. Flag on the dollar test alone. The same goes for accounts that drop to zero, which often signal a missed accrual.
Seasonal businesses
Retail in December or landscaping in spring will trip MoM thresholds every year. Apply the same rule to the year-over-year comparison as well. A change that's large against last month but normal against last year usually just needs a short note rather than a deep investigation.
Subtotals
Apply the rule to revenue, gross profit, operating expenses and net income as well as to individual lines. Small changes across many lines can add up to a material change in total.
The balance sheet
The same two-test rule works for balance sheet accounts, such as receivables, payables, credit cards and loans, compared with the prior month-end. Movements here often explain why cash doesn't match profit.
Tuning thresholds over time
- Review them quarterly. As a client grows, a fixed dollar threshold gets tighter in relative terms.
- Watch the flag count. More than about five flags a month usually means the thresholds are too tight. Zero for several months running means they're too loose, or the client is unusually steady.
- Set them per client, not firm-wide. A $2,500 threshold is meaningless for a $40,000-a-month client and noise for a $2 million one.
- Write them down. Record each client's thresholds alongside the review, so anyone on the team gets the same result.
Frequently asked questions
What is a variance threshold in a monthly review?
A variance threshold is the percentage change from one period to the next that makes a P&L line worth investigating, for example 20% versus last month. It's usually paired with a dollar materiality threshold so that only changes that are both unusual and significant get flagged.
How do I set a materiality threshold for a small business client?
A practical starting point is 1–2% of the client's average monthly revenue, rounded to a simple number. For a client with $150,000 in monthly revenue, that's roughly $1,500 to $3,000. Adjust it after a few months based on how many items get flagged.
Why use both a dollar and a percentage threshold?
A dollar test on its own flags your largest accounts every month on normal fluctuation. A percentage test on its own flags tiny accounts that double from $40 to $80. Requiring both keeps the flags to changes that are unusual and large enough to matter.
Is this the same as audit materiality?
No. Audit materiality is a professional judgement made under auditing standards for an engagement. Review thresholds for monthly management reporting are a practical tool for deciding which movements to explain to a client, and firms set them however suits each client.