Who it's for: anyone who writes or reviews budget-vs-actual commentary for management accounts or a board pack, from finance assistant to financial controller.
What you'll get: the standard variance formulas and sign conventions, a simple structure for each comment, a step-by-step process with thresholds, a worked MonthEndClub Co Ltd example with before-and-after commentary, and AI prompts you can copy.
Reading time: about 9 minutes. Considerably shorter than most variance commentary.
Why commentary gets skipped (and how to stop it)
Most readers of a management pack go straight to the commentary. If it says "costs higher than budget due to higher costs", they stop reading and start emailing questions. Good commentary answers the questions before they're asked: what moved, why, whether it will happen again, and what (if anything) is being done about it. It also saves the finance team a round of follow-ups every month.
Key terms
- Variance: the difference between actual and a comparison figure, usually budget, forecast or last year.
- Favourable (F) / adverse (A): favourable means better for profit (more revenue or less cost); adverse means worse.
- Materiality threshold: the size of variance that needs a comment. Below it, no comment is needed.
- Timing variance: a difference that will reverse in a later month, such as an event moved from November to January.
- Permanent variance: a difference that won't reverse, such as a lost customer or a price increase from a supplier.
- Run-rate: what a line will cost or earn each month going forward if nothing changes.
The formulas and sign conventions
Variance = Actual − Budget
Variance % = Variance ÷ Budget × 100
The common convention is to show each variance so that a positive number is favourable and a bracketed or negative number is adverse. For revenue that's simply Actual − Budget. For costs it's Budget − Actual, so that spending less shows as positive.
Common variations:
- Showing Actual − Budget for every line, with costs positive when overspent, and an F/A column to explain direction. Readers often find this confusing.
- Comparing against the latest forecast rather than the original budget, sometimes both.
- Showing year-to-date variances alongside the month, which helps separate timing from permanent differences.
Whichever convention is used, a one-line key at the top of the table saves confusion. Nothing derails a board meeting quite like a debate about whether brackets are good.
A structure for every comment
A comment that works usually has four parts. Not every comment needs all four, but most need the first three.
| Part | Question it answers | Example |
|---|---|---|
| What | Which line, how much, which direction? | "G&A £4,000 (16%) adverse." |
| Why | What specifically caused it? | "£4,000 of legal fees for October contract work, invoiced late and not accrued in October." |
| Timing or permanent | Will it reverse or repeat? | "One-off; underlying G&A is on budget." |
| So what | What happens next, or what changes? | "Legal now added to the monthly accrual checklist." |
Rules that keep it readable:
- Lead with the number and the cause, not the background.
- Name the driver: a customer, a supplier, a project, a person count. "Higher costs" is not a driver.
- Explain at least 80% of each variance. If the rest is lots of small items, say "other small items" with the amount.
- Use the same order as the P&L.
- Keep each comment to one to three short sentences.
How to write the commentary each month
| Step | What "done" looks like | |
|---|---|---|
| ☐ | Lock the ledger and produce the budget-vs-actual table | Actuals agree to the locked ledger; budget agrees to the approved version |
| ☐ | Apply the materiality threshold to every line | Lines needing comment are highlighted |
| ☐ | Drill into each highlighted line by account, supplier, customer or cost centre | The main driver for each variance is identified with an amount |
| ☐ | Ask budget holders for the business reason where the ledger can't tell you | Reason confirmed by the person responsible, in writing |
| ☐ | Classify each variance as timing or permanent | Each comment says which |
| ☐ | Check whether the variance reveals a close error (missed accrual, mis-posting) | Any error corrected or flagged as a prior-month item |
| ☐ | Write the comments using the what / why / timing / so what structure | One to three sentences per line |
| ☐ | Tick every number in the commentary back to the table | No figure in the text that isn't in the table or the workings |
| ☐ | Get it reviewed by someone who wasn't the preparer | Reviewer sign-off and any changes recorded |
AI shortcut: once you've drilled into the ledger, give an approved AI tool the budget-vs-actual table, the transaction detail for each highlighted line and your notes from budget holders. Ask for draft comments in the what / why / timing / so what structure, one to three sentences each. AI is good at the wording; it can't know the business reason unless you give it. Tick every number it quotes back to the table.
Worked example: MonthEndClub Co Ltd, November
MonthEndClub Co Ltd (fictional) comments on any line where the variance is at least £1,500 or 10% of budget. Positive variances are favourable; brackets are adverse.
| £ | Budget | Actual | Variance F/(A) | Variance % |
|---|---|---|---|---|
| Revenue | 96,000 | 94,500 | (1,500) | (1.6%) |
| Cost of sales | 32,000 | 34,000 | (2,000) | (6.3%) |
| Gross profit | 64,000 | 60,500 | (3,500) | (5.5%) |
| Sales and marketing | 60,000 | 55,000 | 5,000 | 8.3% |
| Research and development | 45,000 | 45,000 | 0 | 0.0% |
| General and administrative | 25,000 | 29,000 | (4,000) | (16.0%) |
| Operating loss | (66,000) | (68,500) | (2,500) | (3.8%) |
Check: (1,500) + (2,000) + 5,000 + 0 + (4,000) = (2,500), which agrees to the operating loss variance. Gross profit: 64,000 − 60,500 = 3,500 adverse, or 5.5% of budget.
What the drill-down found
- Revenue: the budget assumed Customer H (£18,000 ARR) would start on 1 November. Its start date moved to 1 December. That's £18,000 ÷ 12 = £1,500 of November subscription revenue.
- Cost of sales: production hosting was £12,000 against a budget of £10,500, a £1,500 overspend from a one-off data migration for Customer B's upgrade. The remaining £500 is small increases across payment fees and the email delivery API.
- Sales and marketing: a £5,000 conference stand budgeted in November was moved to January.
- G&A: a £4,000 legal invoice for October contract work arrived in November and wasn't accrued in October.
The legal invoice was posted in November:
| Account | Dr | Cr |
|---|---|---|
| Legal and professional fees (G&A) | £4,000 | |
| VAT input tax | £800 | |
| Trade creditors | £4,800 |
VAT is at the UK standard rate of 20%, as at October 2026. Because October was already closed and reported, the cost lands in November. Many teams leave small prior-month items like this in the current month and say so in the commentary, rather than reopening a reported period.
Before: commentary nobody reads
Revenue was slightly below budget. Cost of sales was higher than budget due to higher hosting costs. Sales and marketing was underspent. G&A was over budget due to legal fees. Overall operating loss was worse than budget.
Every sentence is true and none of them helps. There are no amounts, no drivers, and no indication of whether anything will reverse.
After: commentary people actually read
Operating loss £2,500 (3.8%) worse than budget. One-off costs of £5,500 (a late legal invoice of £4,000 and a hosting migration of £1,500) and £500 of small cost increases outweighed £3,500 of net timing benefit (a £5,000 marketing event moved to January, less £1,500 from a delayed customer start). Excluding one-offs, the month is £3,000 better than budget.
Revenue £1,500 (1.6%) adverse. Customer H (£18,000 ARR) moved its start from 1 November to 1 December at the customer's request. Timing only; the contract is signed and December revenue is expected to be on budget.
Cost of sales £2,000 (6.3%) adverse. £1,500 is a one-off data migration for Customer B's upgrade. The other £500 is small increases in payment fees and email delivery costs, in line with higher usage. Hosting run-rate excluding the migration is on budget.
Sales and marketing £5,000 (8.3%) favourable. The conference stand budgeted for November moves to January. Timing only; full-year spend is unchanged.
G&A £4,000 (16.0%) adverse. Legal fees for October contract work, invoiced late and not accrued in October. One-off and relates to the prior month; underlying G&A is on budget. Legal has been added to the monthly accrual checklist.
R&D is on budget, so it has no comment. The reader can see at a glance that the month is £2,500 behind but the underlying run-rate is close to plan.
If you report under US GAAP (ASC 606)
Variance commentary is management reporting, so the approach doesn't change. If revenue variances come from contract changes, the underlying revenue recognition is broadly similar under ASC 606 and IFRS 15 for straightforward subscriptions.
Common mistakes and audit watch-outs
- Restating the table in words. "Revenue was £1,500 below budget" without a reason adds nothing.
- Vague drivers. "Timing", on its own, isn't an explanation. Say what moved and to when.
- Explaining only half the variance. If £4,000 of a £10,000 variance is explained, the reader will ask about the other £6,000.
- Missing the close error. A big variance is sometimes a missed accrual or mis-posting. Fix it, or say so, rather than explaining it away.
- Numbers in the text that don't match the table. The quickest way to lose a reader's trust.
- Unchecked AI wording. AI drafts can sound confident while inventing a reason or quoting the wrong figure. Every reason comes from a person who knows, and every number is ticked back.
- Customer or payroll detail pasted into unapproved AI tools. Only use tools your company has approved for financial data.
Tools that can help
Reporting tools such as Fathom and Syft produce budget-vs-actual tables from Xero or QuickBooks and leave space for commentary. Planning tools and NetSuite reports do the same for larger teams. Many teams draft in Excel or Google Sheets next to the numbers, so every figure is one click from its source. An approved AI assistant helps with first drafts. None of them replace the drill-down or the conversation with the budget holder.
AI prompts to try
Use these only in AI tools your company has approved for financial data. A person reviews every output.
- Find what needs a comment. Give it: the budget-vs-actual table and your threshold. Ask: "List every line where the variance is at or above £X or Y% of budget, with the variance and percentage, using the sign convention in the table key." Check: against your own highlighted lines.
- Find the drivers. Give it: the transaction listing for one highlighted line, this month and last. Ask: "Group these by supplier or customer and show the three biggest differences from last month and from budget." Check: totals agree to the ledger.
- Draft the comments. Give it: the table, the drivers and your notes from budget holders. Ask: "Write one to three sentences per highlighted line: what moved, why, whether it is timing or permanent, and what happens next. Use only the reasons in my notes." Check: every number and every reason.
- Tighten the draft. Give it: your draft commentary. Ask: "Cut this by a third without losing any number or reason. Flag any sentence that doesn't explain a cause." Check: nothing important was dropped.
- Spot the close error. Give it: the variance table and last month's accruals list. Ask: "Which variances could be explained by a missed or reversed accrual from last month?" Check: each suggestion against the ledger before acting.
Rates, thresholds and rules in this guide
Figures were checked against the pages below in October 2026. They change regularly (often each April or at Budget time), and we can't guarantee they're still current or right for your situation. Always check the official page before relying on them.
- VAT rates (GOV.UK): the UK standard VAT rate of 20%
Key takeaways
- Variance = Actual − Budget for revenue, Budget − Actual for costs, so positive always means favourable. Put a key on the table.
- Each comment covers what, why, timing or permanent, and so what, in one to three sentences.
- Name real drivers with amounts, and explain most of each variance.
- A large variance can be a close error; check before explaining it.
- AI is useful for finding drivers and drafting; reasons come from people and every number is ticked back.
FAQs
What materiality threshold is typical?
Many teams use a combination of an amount and a percentage, such as "£X or 10% of budget". The amount usually scales with the size of the business. Some set a lower threshold for revenue than for costs.
Should commentary compare to budget or forecast?
Both are common. Budget shows performance against the original plan; the latest forecast shows whether the most recent expectations held. Many packs show both, with commentary focused on the one the board cares about most.
How long should commentary be?
As short as possible while still answering what, why and whether it will continue. For a small SaaS business, half a page for the P&L is often enough.
Can AI write our variance commentary?
It can write a good first draft if you give it the table, the drivers and the business reasons. It can't know why a customer delayed or why a supplier invoice was late. A person supplies those reasons, checks every number and signs off before the pack goes out.
Related guides
- Monthly Management Accounts and Board Pack Layout
- Accruals and Prepayments: A Practical Guide with Examples
- Reforecasting Without the Pain
- How to Build an ARR Bridge (New, Expansion, Contraction, Churn)
More in Metrics and Reporting guides.
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This guide is general information about common practice. It isn't tailored to any business, and standards, tax rules and figures change. Check your own circumstances, the latest rules and, where needed, a qualified professional before acting.
Last reviewed: October 2026.