What is month over month (MoM) growth? Formula, examples and pitfalls

What is month over month growth?

Month over month (MoM) growth is how much a metric changed from last month to this month, as a percentage of last month.

MoM growth = (this month − last month) ÷ last month × 100%

Sample: a site had 11,000 visitors in September and 12,400 in October. MoM growth = (12,400 − 11,000) ÷ 11,000 = 12.7%. A drop works the same way: 12,400 → 11,800 is −4.8%.

Three things that distort MoM

Months are not the same length. March has 31 days and February 28, so March has 10.7% more days. A metric that did not change per day still shows about +10.7% MoM. Compare daily averages (or the first 28 days of each month) when lengths differ.

Seasons repeat. A shop's December beats November every year; a B2B site dips in August. MoM then measures the calendar, not your work. Use year over year (this October vs last October) for seasonal metrics.

Small bases swing wildly. Going from 20 to 30 sign-ups is +50% MoM. On small numbers, report the counts next to the percentage.

Growth over several months: CMGR

Monthly rates do not average simply. If a metric goes from 10,000 to 13,000 over six months, the compound monthly growth rate (CMGR) is:

CMGR = (13,000 ÷ 10,000)^(1/6) − 1 = 4.47%

Growing 4.47% every month for six months gets you exactly from 10,000 to 13,000. A simple average of six noisy monthly rates usually will not.

A sample report

Sample data. Per day, traffic grew a steady 2% each month. The totals make February look like a slump and March like a breakout. Neither is true.

Watching MoM changes in TapCub

Set the comparison in the date picker to the previous period, and use a monitor with a period change rule to be told when a metric such as visitors or sessions moves by more than a threshold against the previous period. Mark launches and campaigns with annotations so a jump can be explained later. Monitors are described in monitor.

See also

• How do I compare date ranges?