How this instrument works
Month-over-month change measures how far a number moved from one period to the very next one, expressed as a percentage of where it started. The formula subtracts the previous value from the current one, then divides by the previous value — dividing by the starting point, rather than the ending point, is what turns a raw dollar difference into a rate you can compare across periods of wildly different scale. A move from $10,000 to $11,000 and a move from $1,000,000 to $1,100,000 are both a 10% increase, even though the dollar gap differs by two orders of magnitude.
SaaS operators, e-commerce sellers and the finance staff who prep board decks lean on this figure because it is the fastest read on momentum available — a single period closes long before a fiscal quarter does, so a stalling number shows up here first. It differs from year-over-year growth, which compares the same period twelve months apart and cancels out seasonal patterns but reacts slowly, and from a compound annual growth rate, which smooths many periods into one long-run figure and hides exactly the short swings this instrument is built to expose.
A single reading is noisy on its own: a large one-off invoice, a marketing push that pulled sales forward from the following period, or simply a 28-day February set against a 31-day January can swing the percentage without any real change in the underlying business. Practitioners plot several consecutive readings rather than reacting to one, and treat a run of two or three matching results as a trend worth acting on.
- Enter this period's figure in Current month value, $ — revenue, active users, expenses, or any number you track over time.
- Enter the same metric for the prior period in Previous month value, $.
- Read the result in Month-over-month change, % — a positive number means growth, a negative one means contraction.
- Recalculate at the close of each period so you build a running series, rather than judging the business on one number alone.
Worked example — revenue climbs from $100,000 to $110,000
A startup closes June with $100,000 in revenue and July with $110,000. Feeding previousValue = $100,000 and currentValue = $110,000 through the formula gives (110,000 − 100,000) ⁄ 100,000 × 100 = 10.0%, a double-digit increase that would show up on this instrument weeks before the quarterly numbers confirm it.
That single 10% reading is worth checking against the period before it. If June itself only grew 2% over May, July's jump to 10% is a genuine acceleration worth investigating — a new sales rep, a price change, a seasonal spike. If June also read 10%, the business is compounding at a steady clip, and the number stops being a surprise and starts being a pattern.
Questions
Why divide by the previous value instead of the current one?
Dividing by the previous value anchors the result to where the metric started, which is the plain meaning of 'percent change' — dividing by the current value instead would compute something closer to a discount rate and would understate growth. Standard growth-rate conventions, from CPI to GDP releases, anchor to the earlier period for the same reason.
How is this different from year-over-year growth?
Month-over-month compares two adjacent periods, so it reacts to the newest data the fastest — useful for catching a change in direction early. Year-over-year compares the same period twelve months apart, which cancels out seasonal patterns like holiday spikes but reports the news a year late. Fast-moving teams typically watch both: this figure for the immediate signal, year-over-year to confirm it isn't just seasonality.
Why did my result come out negative?
A negative result simply means the current value is smaller than the previous one — the subtraction produces a negative number before it is divided by the previous value. A drop from $100,000 to $90,000, for example, returns exactly −10%. The sign is informational, not a flag; keep it in the figure rather than reporting only the size of the move.
Can this be used for numbers other than revenue?
Yes — the formula only needs both figures to measure the same thing at two points in time. Active users, website sessions, headcount, ad spend and inventory levels all work; enter whichever metric you track as the current and previous values. The one thing that cannot change between the two entries is the definition of what is being counted.
Why shouldn't I react to a single reading on its own?
One period's change absorbs any one-off event that happened to land inside it — a large invoice, a marketing push, a billing-cycle quirk, or simply a shorter calendar month. Comparing several consecutive readings, rather than the latest one alone, separates a real shift in trend from ordinary short-term noise.
What happens if the previous period's value is zero or negative?
The formula is undefined at zero, since dividing by zero has no result, and a negative previous value produces a percentage that reads backwards from what most people expect. This instrument requires the previous value to be greater than zero; if the prior period was genuinely zero, report the dollar change directly instead of a percentage.
References
- U.S. Bureau of Labor Statistics — CPI Frequently Asked Questions
- U.S. Small Business Administration — Manage your finances
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.