The rule is different for each drug, so check which one you are on before you do anything.
For Ozempic: take it as soon as you remember, as long as it has been 5 days or less since your missed dose. Past 5 days, skip it and take your next dose on your regular scheduled day. Never take two doses within 48 hours of each other.
For Wegovy: if your next scheduled dose is more than 2 days away, take the missed one now. If it is less than 2 days away, skip it and just take your next dose as scheduled.
For Mounjaro or Zepbound: you have a 4-day (96-hour) window to take the missed dose. Past that, skip it and resume your normal schedule. Either way, doses need to stay at least 3 days apart, since tirzepatide has a long half-life and stacking doses too close together mostly just adds nausea, not extra results.
If you have missed more than 2 weeks of doses on any of these, call your prescriber before restarting. Going back in at your old dose after a long gap can hit harder than you expect. Once you are back on schedule, Calqulate.net's GLP-1 Dose Calculator can help you sanity-check your titration timeline.