The comparison needs three separate numbers
A price can describe the amount collected at renewal, the cost assigned to a period of service, or a monthly equivalent used for comparison. Those quantities answer different questions. The service-cost calculation helps compare plans across intervals; payment dates help plan cash. NIDDK recommends asking about total program cost and additional fees. [1] Start with our GLP-1 billing checklist to identify the amount, interval and included services before doing arithmetic. A supply described as four weeks does not prove that billing also recurs every four weeks.
Method: count the payment dates, then count the days
This is an original deterministic calculation, not a survey of patient bills. Assume uninterrupted service, advance collection at enrollment on day zero, renewal every 28 days, constant prices and no fees, discounts or pauses. Count payment dates in the half-open interval from day zero through just before day 365. They occur on days 0, 28, 56, 84, 112, 140, 168, 196, 224, 252, 280, 308, 336 and 364. That is fourteen dates. The next charge is day 392. Thirteen periods cover only 364 days; the fourteenth payment buys the period beginning on day 364.
A hypothetical $200 price illustrates the difference
| Measure | Every 28 days | Calendar monthly |
|---|---|---|
| 365-day service-cost equivalent | $2,607.14 | $2,400.00 for 12 monthly periods |
| Average per calendar month | $217.26 | $200.00 |
| Cash collected inside first 365 days | $2,800.00: 14 advance charges | $2,400.00: 12 monthly charges |
| What the last charge covers | Days 364–391 | The twelfth monthly service period |
Calendar-month comparison assumes enrollment on a valid recurring calendar date and twelve payments before its first anniversary. Rounding is to cents; the 365-day model excludes leap years.
Why the $2,800 total is not a 365-day service price
Fourteen $200 payments purchase 392 days under these assumptions. At the end of day 365, 27 paid days remain beyond the measurement window. Dividing $2,800 by twelve would report average first-year cash outflow, not the normalized monthly service price. The service equivalent instead uses $200 × 365 ÷ 28 ÷ 12. That difference matters when comparing a newly enrolled patient with someone already paying for part of the opening period. A paused plan, a delayed shipment, insurance billing or an early authorization can change actual dates. Use the billing-interval calculator for your quote and retain a separate dated payment schedule.
A real disclosure shows why the interval matters
The Found review describes an offer whose terms explicitly use 28-day billing. The same offer document defines a twelve-month generics or branded-membership term as 48 weeks. [2] Those examples show why both interval and total term belong beside a monthly headline. They do not establish the duration of every product or plan. A 48-week term equals 336 days, which is 29 days shorter than a 365-day year. Do not silently turn it into twelve calendar months or assume one additional four-week purchase reaches the anniversary: 48 plus four weeks is 364 days.
Use dates to compare your own two offers
Record enrollment, the first regular renewal and the prepaid end date. Ask whether payment authorizes a prescription review, a shipment or a period of platform access. Then compare the same product and services over the same horizon. Our two-plan budget comparison helps organize recurring and one-time costs, while the prepaid-plan analysis adds the consequence of stopping before a longer term is used. Leave unknown laboratory or pharmacy charges unresolved rather than assigning zero. A mathematically cheaper plan still requires appropriate clinical care and a prescription decision.