Key points
Flux analysis compares actual balances between two periods and explains every change above a set threshold.
It differs from variance analysis, which compares actuals to budget or forecast.
Use both a dollar and a percentage threshold, and always flag lines that change sign or start from zero.
Good commentary names the drivers, sizes each one, and the drivers add up to the total change.
At usage-based companies, revenue and cost of revenue should move together; when they do not, gross margin is the story.
What flux analysis is
Flux analysis compares account balances between two periods, flags changes above a threshold, and explains each one in writing. It runs at the end of the close, after entries are booked and before results go to leadership. The explanation is the product; the variance table is just the starting point.
Done well, it catches errors the reconciliations missed. A missing accrual, a misclassified bill, or a revenue release that never posted all show up as a change nobody can explain.
Flux analysis vs variance analysis
Flux analysis | Variance analysis | |
|---|---|---|
Compares | Actual to actual: this month vs last month, or vs same month last year | Actual to budget or forecast |
Main question | Is the accounting right, and what changed? | Are we on plan, and why not? |
Owner | Accounting, during the close | FP&A, after the close |
Covers | P&L and balance sheet | Mostly P&L and cash |
Setting thresholds
Most teams flag a line when it crosses both a dollar and a percentage threshold. The dollar floor stops tiny accounts from creating noise; the percentage stops large stable accounts from hiding real movements.
Line type | Example threshold | Why |
|---|---|---|
Revenue and cost of revenue | Over $10,000 and over 10% | Drives gross margin, the number boards ask about |
Operating expense lines | Over $15,000 and over 15% | Lumpier by nature: hiring, events, legal |
Balance sheet accounts | Over $25,000 and over 10% | Larger balances, slower to move |
Any line that changes sign or goes from zero | Always | Often a mispost or missing entry |
These are starting points, not rules. The SEC staff's guidance on materiality in SAB 99 says a percentage threshold can be a first screen but cannot be the only test. Small amounts can still matter, for example if they flip a trend.
Worked example: October P&L flux
Fieldnote AI, a fictional Series B company with usage-based pricing, compares October to September. The numbers are illustrative. Threshold for revenue and cost lines: over $10,000 and over 10%.
Line | September | October | Change | % | Comment needed |
|---|---|---|---|---|---|
Subscription revenue | 290,000 | 300,000 | 10,000 | 3.4% | No |
Usage revenue | 140,000 | 176,000 | 36,000 | 25.7% | Yes |
COGS: cloud inference | 96,000 | 130,000 | 34,000 | 35.4% | Yes |
COGS: hosting and support | 14,000 | 14,000 | 0 | 0.0% | No |
General and administrative | 80,000 | 104,000 | 24,000 | 30.0% | Yes |
Gross margin | 74.4% | 69.7% | (4.7 pts) | Yes |
Writing flux commentary
A useful comment names the driver, sizes it, and says whether it will recur. Here is the comment for cloud inference cost.
COGS: cloud inference up $34,000 (35.4%). Higher customer volume added $30,000, in line with usage revenue. A shift toward a newer, higher-cost model added $12,000. A reserved-capacity discount starting October 1 saved $8,000. Gross margin fell 4.7 points to 69.7%. Expect the volume and model-mix effects to continue; pricing for the newer model is under review. Support: cloud invoice and usage export by model.
And for usage revenue:
Usage revenue up $36,000 (25.7%). Two customers moved production workloads live mid-month: Customer A added $18,000 and Customer B $11,000. The remaining $7,000 is spread across the base. No price changes. Both customers are on 12-month commitments, so this should hold. Support: metering export priced at contract rates.
Compare that with the comment most teams write: "Increase due to higher usage." It is true, unsized, and tells a reviewer nothing they could test. The drivers in a good comment should add up to the change. In both examples above, they do.
Do not skip the balance sheet
P&L flux gets the attention, but balance sheet flux catches more errors. Watch for deferred revenue that grows while billings are flat, accrued expenses that never decline, or prepaid balances that stop amortizing. Each points to an entry that was missed or not reversed.
How auditors read your flux
Auditors run their own analytical procedures under PCAOB AS 2305 for public company audits, and similar standards for private ones. An article in The CPA Journal notes that a prior-year comparison alone is usually not an adequate expectation for audit purposes. Your flux is not their test, but a clear one with sized, supported drivers shortens their work and their question list.
Common mistakes
Drivers that do not add up. If the explained pieces total $20,000 of a $34,000 change, $14,000 is still unexplained.
Explaining with the account name. "Legal costs rose because of legal fees" restates the line.
Comparing only to last month. Seasonal lines need the same month last year too.
Running flux before entries are final. Late adjustments change the numbers and make the comments wrong.
Ignoring margin. At usage-based companies, revenue and cost of revenue should move together. When they do not, find out why.
How Quanta handles flux
Quanta tags COGS lines and builds integrations into usage databases and cloud bills, so cost of revenue can be split by driver rather than read off a single invoice. Finance leads can ask questions of their books in Claude through the Quanta MCP, such as which customers drove a change, and the answer traces back to journal entries.
Quanta perspective
For usage-based companies, the most important flux is not revenue; it is the gap between usage revenue growth and compute cost growth. When cost grows faster, margin erodes quietly, often from model mix rather than volume. Split cost of revenue by driver every month and the flux comment almost writes itself.
Frequently asked questions
What does flux mean in accounting?
Flux means fluctuation: the change in an account balance from one period to another. Flux analysis is the review and explanation of those changes.
What is a typical flux analysis threshold?
Many teams flag lines that change by more than a set dollar amount and a set percentage, such as $10,000 and 10%. The right numbers depend on company size and materiality, and should be documented.
Is flux analysis required?
No standard requires a company to perform flux analysis. It is a common close control, and auditors and reviewers expect to see it in a well-run close.
Should flux analysis cover the balance sheet?
Yes. Balance sheet flux often catches missed accruals, unreversed entries, and stalled amortization that the P&L view hides.
Who reviews flux commentary?
Usually the controller reviews the accountants' comments, and the CFO or head of finance reviews the summary before results go to the CEO or board.