Weeks to Months

The Flight Plan Is Built in Weeks; the Board Deck Asks for Months

Campaign work is scheduled in weeks because that is the grain everything else runs on: media buys are booked by week, creative rotations are swapped weekly, email cadence is weekly, and the reporting dashboard has a week-over-week column that everyone reads first. Then the quarterly review arrives and asks how many months the activity covered, because budget lines, invoices and the finance system close monthly. Two calendars, one campaign, and the translation between them is not clean.

The mismatch is small enough to ignore for a single flight and large enough to cause an argument at year end, when a plan built from four-week blocks turns out to have overrun the twelve months it was supposed to fit inside.

Conversion factor: 1 wk = 0.22998419 mo on this page's fixed month of 30.436875 d, so a month holds 4.348125 wk. A 13-week flight is 2.9897945 mo — near enough a quarter to report as one. A four-week flight, however, is only 0.91993675 mo: eight per cent short of the month it is usually called.

Why Two Calendars Run Side by Side

Delivery happens on a weekly grid

Insertion orders, creative rotations, send schedules and stand-up reviews all land on the same weekday every time. A week is the smallest unit a campaign can genuinely be re-planned in, which is why the working calendar never leaves it.

Money closes on a monthly grid

Budget releases, agency invoices, accruals and the numbers a board sees are all monthly. Nobody is going to re-cut the ledger into weeks, so the weekly plan has to be expressed in months at the moment it meets finance.

Four weeks is not a month

Calling a four-week burst "a month" quietly loses two and a half days each time. Repeat it through a year of always-on activity and thirteen of those blocks fit where twelve months were budgeted — one extra flight nobody funded.

The year holds 52.1775 weeks

Not 52. The stray fifth of a week is why annual plans drift a day or two against the calendar each year, and why a fiscal calendar occasionally has to insert a 53rd week to catch up.

Getting a Weekly Plan Into a Monthly Report

The work is quick, and it is worth doing before the deck is built rather than in the meeting where somebody challenges the total.

Enter the flight length in weeks

Put the week count in the left field and the month figure follows as you type. A six-week launch push comes back as 1.37990513 mo — which is what to say when the answer "about six weeks" gets pushed for a monthly number.

Add the phases nobody counts

Brief, creative development and legal review sit in front of the live dates and belong in the same total. Three weeks of pre-production plus a six-week burst is nine weeks, or 2.0698577 mo — over two months of calendar for a campaign described as six weeks long.

Reverse it when the budget comes first

Hit swap (↔) to run mo → wk when finance releases a window instead of a plan: a three-month allocation is 13.044375 wk of activity to fill. Both fields accept typing, so a month figure entered on the right resolves the weeks without switching direction at all.

Move the number into the plan

Copy puts the bare figure on the clipboard, with no unit and no grouping, so a pacing sheet or campaign tracker sums it instead of treating it as a label. Pasted values with stray spaces are read fine on the way in, too.

The month here is a fixed 30.436875 d, not the month on your wall. Real months run 28 to 31 days, so a four-week flight is a whole month of February and four days short of a month of July. For pacing a named month, count its actual days; use this fixed average for plans, ratios and anything that spans several months.

A Campaign Calendar Read in Both Units

Typical phases of a launch and always-on programme, with the month figure each one produces on the 30.436875-day average and what a monthly report tends to do with it.

Campaign phase	Weeks	Months (30.44 d)	What the monthly report shows
Teaser / warm-up	2 wk	0.45996838 mo	Half a month of spend, usually split across two reporting periods
Brief to approved creative	3 wk	0.68995257 mo	Agency fees land before any media cost appears
Four-week burst	4 wk	0.91993675 mo	Reported as "a month" and under-states the year by 8 %
Launch push	6 wk	1.37990513 mo	Straddles a month end; peak spend rarely sits in one period
Seasonal peak window	8 wk	1.83987351 mo	Two heavy months if it starts on the first, three if it does not
Quarter-long sustain flight	13 wk	2.98979445 mo	The clean case — one quarter, three months, no split
Half-year always-on	26 wk	5.9795889 mo	Six budget lines, the last of which is four days short
Annual retainer	52 wk	11.95917781 mo	A twelve-month contract needs 52.1775 wk, not 52

The last two rows are where planning arguments actually start. A 52-week programme finishes about a day and a quarter before the twelve months it was sold as, and a run of four-week bursts accumulates the opposite error — thirteen of them fill the year with a flight the annual budget never allowed for. Whichever way it leans, the fix is the same: decide once whether the plan is anchored to weeks or to months, state which, and convert at the boundary instead of letting each function assume its own.

What This Pair Handles During Planning

A month figure while the flight is still being argued

Nothing to submit — the second field updates on each keystroke, so week counts can be tried against a monthly window live in a planning call rather than after it.

Budget windows converted back to weeks

Type a month figure into the right-hand box and the week count comes back, which is the direction you need when finance hands over a period and asks how much activity fits.

Quarters and years in the same dropdown

Quarter and year sit alongside the month, so a flight can be checked against a fiscal period without leaving the page or converting twice.

Numbers a pacing sheet will accept

The clipboard gets digits only, so the month figure drops into a spend-per-month formula without the cleanup a pasted "1.38 mo" would need first.

What Campaign Planners Ask About Weeks and Months

Why does a four-week flight report as less than a full month?

Because a month averages 30.436875 d and four weeks is only 28. The conversion gives 0.91993675 mo, an eight per cent shortfall, and the missing 2.44 d has to go somewhere. Run four-week blocks back to back through a year and thirteen of them fit inside the 52.1775 weeks available, so a programme budgeted as twelve monthly flights quietly acquires a fourteenth wave of creative, a thirteenth invoice or a gap, depending on which side blinks first. Plan in whichever unit the money is released in, and treat the other as a translation.

Is a quarter thirteen weeks or three months?

Both, within a rounding error, and that is why the quarter is the one boundary where the two calendars behave. Three months is 13.044375 wk and thirteen weeks is 2.98979445 mo — three hundredths of a month apart. Retail and manufacturing calendars exploit this by cutting each quarter into 4-4-5 or 4-5-4 week periods, giving thirteen-week quarters that always end on the same weekday and make like-for-like comparison possible. The cost is that those "months" are 28 or 35 days rather than calendar months, so a 4-4-5 period never lines up with a bank statement.

My media plan uses ISO week numbers but finance reports months — how do I reconcile them?

Accept that roughly one week in four straddles a month boundary and decide the rule in advance. The two workable conventions are to assign a split week to the month containing its Thursday, which is how ISO 8601 already resolves the year boundary, or to apportion its spend across both months by day. Whichever you pick, apply it to every split week rather than case by case, and note it on the plan. Remember too that an ISO year sometimes carries 53 weeks; when it does, a weekly programme has an extra period that no monthly budget has a slot for.

How do I spread a monthly budget across a weekly pacing sheet?

Divide by 4.348125, not by four. A 40,000 monthly budget becomes about 9,199 a week on the average month, whereas dividing by four would pace it at 10,000 and exhaust the allocation with days of the month still to run. The same factor works on impressions, sends and any other monthly target. If you are pacing a named calendar month instead of an average one, use its actual day count — a 31-day month holds 4.4285714 wk and a 28-day February exactly 4, and those two differ by more than a tenth of the budget per week.

What happens to a weekly cadence over a full year?

It drifts, slowly and predictably. Fifty-two weeks is 11.95917781 mo, so a year of weekly activity ends about 1.24 d before the calendar year does, and the following year's schedule starts on a different date unless somebody nudges it. Over four years that accumulates to roughly the extra week fiscal calendars periodically insert. For most campaigns the drift is harmless; it starts to matter for anniversary-anchored activity, seasonal peaks that must hit the same trading dates, and any always-on retainer priced per month but delivered per week.