What is seasonality?

Definition

Seasonality is the predictable pattern of higher and lower periods across the year. On the books, this is a shape in the monthly numbers, not an account and not a posted line.

Where it shows up

P&L: Related to the predictable high and low periods in revenue and expense.

Balance Sheet: Related to the inventory and working-capital swings that follow those periods.

Cash flow: Related to the predictable high and low periods in cash.

See also: Year-Over-Year Growth · Forecast · Revenue

You will not find a seasonality line on the Income Statement. You see it when revenue is $4,000 in January and $16,000 in July, every year.

The Balance Sheet shows the follow-on. Inventory builds before the high months, and working capital tightens when the low months arrive.

Cash follows the same pattern. The high months throw off cash; the low months spend it.

Owners who only watch one month miss the pattern. July always looks like a miracle until you stack five Julys.

A budget that spreads the year evenly will look "over" every summer and "under" every winter. The pattern was never a miss; the plan ignored it.

How it works

Plot the same line by month for a few years. If July is always the peak and January is always the trough, that shape is seasonality.

The pattern can sit in revenue, in expense, or in both. A pool service bills more in July; heating oil does the opposite.

Weather, holidays, school calendars, and buying seasons are the usual drivers. The books do not name the driver; they only show the repeating shape.

Compare July to June and the jump looks huge. Compare this July to last July and you are asking whether the seasonal peak itself grew.

Inventory is bought before the peak so it can be sold during it. That buy shows up as a current-asset build, then as cost of goods when the season hits.

Working capital often thins in the slow months because receipts drop while rent and payroll do not. The low months are when a line of credit actually gets used.

A forecast that ignores the pattern will be wrong twice a year. Build the high and low months into the plan, then judge actuals against that shape.

The general ledger already holds the monthly totals. You are reading a repeating shape, not posting a journal entry.

Internal controls do not create the pattern. They only keep the monthly numbers trustworthy enough to see it.

Example

A pool service bills about $4,000 a month in winter and $16,000 a month in July, every year. That fourfold summer peak is seasonality, not a one-time win.

If this July is $16,000 and last July was $15,000, the seasonal peak grew a little. The $16,000 versus $4,000 winter month is the pattern, not the growth.

Chemicals and extra labor are bought in May and June so July work can happen. Inventory and payables rise before the peak, then fall as the work is billed.

A bank that only sees January may think the shop is dying. Stack three years of Januaries and the low month is normal.

If the owner spreads $120,000 of yearly revenue evenly across twelve months, every winter actual will look short. The budget was the problem, not the winter.

Cash is tight in March even in a good year. The line of credit exists for that trough, not because July failed.

Common mix-ups

Seasonality is not year-over-year growth. Year-over-year growth asks whether this July beat last July; seasonality is the fact that July is always the high month.

Seasonality is not a forecast. A forecast is an updated projection; seasonality is the repeating in-year pattern that a good forecast should include.

Seasonality is not month-over-month growth. Month-over-month growth is the percent from May to June; seasonality is why June is usually bigger than May.

Related terms

• Year-Over-Year Growth: The change versus the same period a year earlier.
• Forecast: An updated projection of where the numbers are actually heading.
• Cash Flow Forecast: A forward projection of cash receipts and payments.
• Revenue: The total value of goods and services the business earned in a period.
• Working Capital: Current assets minus current liabilities, showing short-term operating cushion.
• Budget: The approved plan of revenue and spending for a coming period.
• Month-Over-Month Growth: The change from one month to the next, expressed as a percentage.
• Inventory: Goods held for sale or used to produce goods for sale.