Thirteen Charges, Twelve Months

Thirteen four-week periods is 364 days. Twelve is 336. A year is 365. That mismatch is the whole of this article, and depending which side of it you land on it is worth about one extra payment — or about two months of missing coverage.

Nobody is hiding it. It is written into published terms in plain sight. It is simply that "per month" does two different jobs in the same sentence, and readers assume the calendar meaning.

Pattern one: a four-week month, and a thirteenth charge

Noom prices its microdose program in a footnote that mixes both units: "Initial 3 week subscription and 4 weeks of medication from $49 plus tax and $179 per month plus tax for 12 week subscription thereafter."¹

Read the units. The ongoing plan is a twelve-week subscription priced "per month". Three months to twelve weeks makes a month four weeks long. A year then holds 13 of them, not 12.

That gap is not a fee and not a price rise — it is one more charge at the rate already quoted, which is the hardest kind of increase to notice. Our Noom Med review prices both readings side by side.

Pattern two: the manufacturer counts to thirteen itself

You do not have to infer this one. Lilly's Zepbound savings card terms define the unit and then count it.

The definition: "month is defined as 28-days and up to 4 single-dose pens."²

The count: the card "may be used for a maximum of up to 13 prescription fills per calendar year."²

Thirteen 28-day fills is 364 days — a year, resolved correctly. And the caps reconcile precisely: maximum savings of "up to $100 per 1-month prescription" against a "separate maximum annual savings of up to $1,300 per calendar year", which is $100 × 13.² The manufacturer built its own arithmetic on thirteen.

Pattern three: the same card, eleven fills

The identical program, applied to the KwikPen presentation, allows something different: "Card may be used for a maximum of up to 11 prescription fills per calendar year," with the same 28-day month.²

Eleven 28-day fills is 308 days. That leaves 57 days of the calendar year on which the card cannot be used — on the same product line, under the same program, in the same document. If you are budgeting around a card, the fill count is a harder constraint than the dollar cap, and it is the number nobody quotes. There is more on how these caps behave in copay cards: the cap is the product.

Pattern four: every 30 days

Found bills on a rolling 30-day cycle rather than the calendar month, and prices its plans against 12-month terms paid up front.³

A 30-day cycle produces 365 ÷ 30 = 12.17 charges a year. In practice that means the charge date walks backwards through the calendar — the 4th, then the 3rd, then the 2nd — and a thirteenth charge appears in some years and not others depending on your start date.

This is the least costly of the patterns and the hardest to reconcile against a bank statement, because the anniversary date never repeats.

Pattern five: a month defined by the box

NovoCare defines its month by package rather than by days. Its footnotes state that "one month is defined as 1 box of 4 pens of Wegovy", and for the tablet products, "1 bottle of 30 tablets."⁴

A four-pen box and a thirty-tablet bottle are not the same length of time. That matters because both sit in the same footnote at prices a reader will naturally compare: $199 for two monthly fills of the injectable through 31 December 2026 and then $349, against $149 for the tablet.⁴ Those are two different units of "month", quoted eight lines apart.

The patterns, side by side

Every pattern above resolves the same 365 days, and no two resolve them the same way.

What the remainder is worth, in dollars

The gap is not abstract. It is one charge, and its size is the size of your monthly bill.

On Noom's $179 microdose plan, the thirteenth charge is $179 a year.¹

On a membership at $79 a month, a four-weekly cycle would add $79. At $149 it adds $149.

On Lilly's card, the constraint runs the other way: two fills a year outside the KwikPen card's eleven-fill allowance means two fills at the regular price rather than the discounted one.

None of these are large numbers next to a year of treatment. All of them are large next to the difference between two providers you are choosing between, which is the decision the monthly headline is meant to help you make. Four-weekly billing is common enough at the microdose end of the market that we print the cycle beside the price on the microdose GLP-1 board, where the annual figure already has the thirteenth charge in it.

How to find out which one you are on, before you sign

Two questions, both with short answers if the seller is straight with you.

"How many times will my card be charged in the next twelve months?" Not how much per month — how many charges. The answer is a whole number, and it is either 12 or 13.

"How many days does one charge cover?" Twenty-eight, thirty, a calendar month, or one box. Those are four different products at the same headline price.

Then multiply. The annual total is the only figure that compares cleanly across two providers, which is why our boards for compounded semaglutide and compounded tirzepatide carry a true-year cost rather than a monthly one.

Related: how to read a GLP-1 provider's pricing page and a $169 month that costs $2,028 on day one.