calculateCalculator Guide

GLP-1 Injection Schedule

Once-weekly GLP-1s are forgiving — you have a multi-day window for late doses — but the schedule itself only works if you actually pick a day, write it down, and recover predictably when life gets in the way.

A weekly injection is deceptively simple. You inject one day. You inject the same day next week. You repeat for life, or until you and your provider decide to stop. The complication is not the injection — it is the eleven months of weekdays that look the same, the work trip that ate your Sunday, the prescription that arrived two days late, the dose that did not come out of the pen cleanly.

This page is a system, not a list of tips. The system is: pick a day deliberately, set a recurring reminder, log every dose, and know the recovery rules cold so you do not have to think under stress.

The formula

The injection schedule itself is a single rule: same day every week, ideally within a 2-3 hour window on that day. Both semaglutide and tirzepatide have half-lives long enough that morning vs evening barely matters at steady state. What matters is consistency week to week.

The recovery rules are different by drug. For semaglutide (Ozempic, Wegovy), if your dose is late by less than 5 days, take it as soon as you remember and resume the regular schedule. If it has been 5 days or more, skip the missed dose entirely and take the next one on the regularly scheduled day. For tirzepatide (Mounjaro, Zepbound), the window is 4 days, not 5 — if you are within 4 days, take it; beyond 4 days, skip.

If you find yourself needing to permanently shift injection days (Monday no longer works, Friday is better), the rule is: there must be at least 72 hours between the last injection and the new injection day. That gap is to avoid stacking doses and increasing side effect risk.

The Rule

Inject same day weekly. Late <5 days (sema) or <4 days (tirz) → take ASAP. Later → skip.

When shifting injection days permanently, allow at least 72 hours between the last dose and the new day.

Worked examples

Scenario A: Semaglutide, regular Sunday dose, forgot until Wednesday

Three days late, within the 5-day window. Take it Wednesday, resume Sundays the following week. Side effects may bunch up slightly mid-week — eat lightly.

Scenario B: Tirzepatide, regular Monday dose, remembered next Saturday (5 days late)

Outside the 4-day tirzepatide window. Skip the missed dose, take the next one on the normal Monday two days later. Do not double up.

Scenario C: Shifting from Friday to Sunday permanently

Take Friday's dose as normal. Skip the next Sunday (only 48 hours, too soon). Take the dose the following Sunday (9 days after Friday). Continue Sundays thereafter.

How to actually track this: a simple calendar reminder is enough for most people. The more durable system is a physical or digital log with three columns — date, dose, site (left abdomen, right thigh, left arm, right abdomen, etc.) — rotated to avoid lipohypertrophy. Apps like the Mounjaro and Wegovy patient apps, or generic tools like MySymptoms or Stridelnk, work too. The medium does not matter; the consistency does.

How to pick a day: choose the day where you are most likely to remember and least likely to have a heavy social calendar. Many people pick Sunday evening — you are home, the week ahead is predictable, and any peak side effects land on workdays where you control your eating. Avoid Friday and Saturday if you have an active social life — peak nausea + a dinner out is not a fun combination.

Where the calculator will live

An interactive injection tracker — where you set your day, log doses, get late-dose decision guidance, and see your dose-on-time streak — is on the roadmap. Until then, the manufacturer apps for Wegovy and Mounjaro both include basic dose tracking, and a recurring calendar reminder labeled with the dose strength works for most people.

Common questions

Common Concerns

Does the time of day matter?expand_more

Less than people think. Both semaglutide and tirzepatide have half-lives measured in days, not hours. Morning vs evening is a personal-preference question. Many users prefer evening injections because peak side effects happen 12-36 hours later — sleeping through some of that helps. If you inject in the morning, expect peak GI side effects the following evening or the day after.

What if I lose a dose to a bad injection (squirted out, broken pen)?expand_more

If a meaningful amount of medication clearly did not enter your body, contact your pharmacy or prescriber the same day. Most will either replace the pen or instruct you to take a replacement dose. Do not just inject a second time without guidance — partial absorption is hard to estimate.

Can I split a weekly dose into two half-doses?expand_more

No. The drugs are designed and dosed around once-weekly pharmacokinetics. Splitting doses changes peak and trough concentrations, can change side effects, and is not how the medications were studied. Some providers do prescribe smaller doses (micro-dosing) on a weekly schedule for tolerance, but the cadence stays weekly.

What if I'm traveling across time zones?expand_more

Time zones do not matter — the dose interval matters. If you injected on a Sunday at home, inject the following Sunday in your destination, regardless of local time. A few hours of timezone-driven drift over many weeks is clinically meaningless.

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