MosoFin skill · budget-vs-actual-analysis · learning guide

From one line over budget to commentary with an owner

This page shows how the skill compares a month with its budget, one level at a time. It starts with one line and two numbers. It ends with commentary that names an owner. The page quotes every rule from the skill itself and works every number in front of you.

The rules are the skill's ownThe page quotes each rule word for word, with the file and section it comes from.
Outside sources back the factsThey are an SBA page, two SEC texts, an open accounting textbook and a GAO tool. Each one has a number and a link.
The page shows the mathOpen "Check it yourself" on any level. Follow every line on a calculator.
Your numbers, your checkAt the end, enter your own month. The page runs Steps 2 to 5 on it.
Rule: quoted from the skill Fact: from a cited authority, numbered like 1 Example: made-up figures, calculated in full
How it thinks

Fifteen rules the whole skill runs on

Every level below applies one or more of these rules. The examples use one made-up company, Northbrook Trading, a US entity that keeps its books in US dollars. Its fiscal year is the calendar year. The page compares its September actuals with the "FY26 Board Budget". Its thresholds are $5,000 and 10%. These figures are the company's own choices. No standard sets them.

Learning path

Six levels, from simple to complex

Check it yourself

Put in your own month

Enter up to eight lines from your own month, or load the example. The page runs Steps 2 to 4 from references/method.md in part 1 and the Step 5 split in part 2. The page sends nothing anywhere.

Part 1: the variance on each line

LineTypeBudgetActual

The zero-budget rule for "both": a line with a budget of $0 has no percent. Under "both", this page counts that line as passing when its dollar variance passes the dollar threshold. This rule is the page's own choice. The skill does not state one. If you leave both thresholds empty, the page applies no rule. It ranks every variance by its dollar size, as the skill does when you decline to set thresholds.

The page computes variance = actual − budget, and percent = variance ÷ |budget|. A revenue line is F when the actual is higher. An expense line is U when the actual is higher. The "Northbrook, September" preset gives a net effect on profit of −$23,900 U. It needs commentary on 6 of 7 lines under "either" and on 4 of 7 lines under "both".

Part 2: volume and price

Budget
Actual

Volume = (actual units − budget units) × budget price. With one product, the budget average price is the budget price. Price = (actual price − budget price) × actual units. With one product and one currency, mix and FX are zero, so the two parts add to the total variance. The page shows the unexplained difference, which is $0 here. The "Northbrook revenue" preset gives volume +$60,000 F and price −$28,000 U, a total of +$32,000. A split from this calculator shows the arithmetic only. A person still gives the cause.

Using it

What it asks, needs and gives back

Asks firstDo you want to use Mosofin for this run, or upload the data yourself? Which entity? Which period, at what grain, and is that period closed? Which budget, by name? What are your materiality thresholds, as an amount and a percentage, and must a variance pass both or either? Which one-time items fall in the period? Which driver data do you have? Which grouping does management read?
NeedsThe skill needs the actuals and the named budget, by line and by month. An uploaded budget also states its basis, cash or accrual, and any split by class, location or customer. The prior-year actuals, the chart of accounts and the driver data make the result better. You type in the thresholds and the one-time items, because no ledger holds them.
Gives backThe skill gives back six sheets: the variance summary, the commentary, the driver detail, the full-year outlook, the waterfall data and a coverage sheet. If the period is not closed, the summary header says "PRELIMINARY". The skill asks before it makes an Excel file.
NeverThe skill never revises a budget, posts a reclassification or updates a forecast. It never chooses the period, the budget version, a threshold or the entity for you. It never invents a cause. It never saves the figures, the commentary or the outlook.
Sources

Where every fact on this page comes from

The rules are the skill's own. The facts below come from five outside sources. They are an SBA page, the SEC's Item 303 rule, the SEC's 2003 guidance on MD&A, an open accounting textbook and a GAO tool. MosoFin checked each one on 27 October 2026 from search results and did not open the pages. Follow the link for today's wording.

    Not backed by an outside authority. The six stages, the F/U table and the six output sheets are the skill's own. The "either" materiality rule and the $5,000 and 10% thresholds are Northbrook's made-up choices. MosoFin made up all figures in the examples. The zero-budget rule for "both" in the calculator is this page's own choice. The page marks them where they appear.