Where to inject

Three areas, one rule about the navel, and a reason to rotate that almost nobody bothers to explain.

The three areas

Dashed red: the two inches around the navel to stay out of. Shaded: fair game.

Area	The detail that matters
Belly	The usual choice, and the easiest to reach with your other hand free. Stay at least two inches — five centimetres — clear of the navel in every direction. The tissue right around it behaves differently.
Outer thigh	Front and outer, roughly the middle third between hip and knee. Not the inner thigh.
Back of the upper arm	The fleshy part at the back. Easy if someone else is doing it, awkward if you're doing it yourself — most people who use this site have help.

Why rotation is a real instruction and not a formality

Inject the same square inch every week for long enough and the fat under it thickens into a firm patch. It's called lipohypertrophy. Two things then happen: the lump doesn't go away quickly, and — the part that matters — absorption from a lump is unpredictable.

So you inject your correct, carefully calculated dose into tissue that delivers some unknown fraction of it. You get an unexplained bad week, or an unexplained flat one, and nothing about your arithmetic or your vial was wrong. That's the failure mode rotation prevents. It isn't about comfort.

Which is also why you don't inject into a lump you can already feel, and why it's worth running a hand over the area first.

An eight-week rotation

Any system beats no system. This one just goes round in order and comes back to the start after two months, which is long enough for anywhere to recover.

Same day every week, next spot down the list. Print it, tick it, don't think about it.
Week	Site	Week	Site
1	Belly, lower left	5	Left thigh, outer
2	Belly, lower right	6	Right thigh, outer
3	Belly, upper left	7	Left arm, back
4	Belly, upper right	8	Right arm, back

Only using your belly? Quarter it and go round the four quadrants — that's still four weeks between repeats, which is enough.

Things that make it hurt less

Let the alcohol dry. Injecting through wet alcohol is the single most common reason a shot stings, and it's entirely avoidable. Ten seconds.
Take it out of the fridge first. Twenty to thirty minutes to reach room temperature. Cold liquid stings going in.
Go in decisively. Slow entry hurts more than quick entry.
Skip anywhere that's bruised, scarred, or stretch-marked. Same absorption argument as the lumps.

The dose itself: the calculator · tirzepatide chart · semaglutide chart.