What is month over month (MoM)?

Month over month (MoM) compares a figure for one month with the same figure for the month before, as a dollar change and a percentage change. It shows the most recent movement in revenue, costs or profit.

How it is calculated

MoM change = this month - last month

MoM % = MoM change / last month × 100

How it is used

MoM is the first comparison most people look at in a monthly review. It is quick to read and catches errors early: a missing rent bill or a doubled invoice usually shows up as an odd MoM swing. It is also the noisiest comparison. Seasonal sales, the number of working days and payroll timing all move it. With bi-weekly payroll, two months a year have three pay dates instead of two, and wages jump for no real reason.

Worked example

LineSeptemberOctoberMoM $MoM %
Revenue$40,000$48,000+$8,000+20.0%
Wages$30,000$31,500+$1,500+5.0%
Office supplies$100$400+$300+300.0%

Revenue is the line worth explaining. Office supplies has the biggest percentage but only a $300 change, which is why most reviews pair the percentage with a dollar threshold.

Common mistakes

  • Reading a seasonal swing as a trend. Check year over year before telling a client sales are falling.
  • Percentages on tiny bases. A move from $100 to $400 is 300% and still not material.
  • Dividing by a negative or zero. If last month was a loss or zero, show the dollar change and skip the percentage.
  • Ignoring one-offs. An annual insurance premium booked in one month distorts MoM unless it is spread as a prepaid expense.

Related terms

  • Year over year (YoY): Year over year (YoY) compares a figure for a period with the same period one year earlier, such as October 2026 against October 2025.
  • Trailing twelve months (TTM): Trailing twelve months (TTM) is the total of a figure, such as revenue or net income, for the most recent 12 consecutive months.
  • Materiality threshold: A materiality threshold is the size of change, or error, that is big enough to matter to the people reading the numbers.
  • Percentage points vs percent: A percentage point is the simple difference between two percentages, while a percent change is that difference relative to the starting value.

Further reading