Is toothpaste with glycerin halal?

Usually yes. Glycerin (also called glycerol) is a common ingredient in toothpaste, and most of it comes from plants or is made synthetically. Even when it comes from animal fat, you don't swallow toothpaste, and many scholars are relaxed about it. If you want complete peace of mind, choose a toothpaste that says "vegetable glycerin" or carries a halal label.

What is glycerin?

Glycerin is a clear, sweet, syrupy liquid that keeps toothpaste smooth and stops it drying out. It can be made from three kinds of sources:

Plants: palm, coconut or soy oil. This is the most common source today.
Animal fat: usually beef or sheep tallow, but in theory it could be pork fat.
Synthetic: made from petroleum-based chemicals in a lab, with no animal involved.

A label saying only "glycerin" doesn't tell you which. Brands in Europe and the USA often don't say unless asked.

Why most scholars aren't worried

It isn't food. The rules on forbidden ingredients are about eating. You spit toothpaste out and rinse your mouth, so there's no intention to swallow.
Transformation: glycerin is a refined chemical, and many scholars hold that when a substance is fully changed into something new (istihalah), the new substance is not treated as the original one.
Doubt about the source: if you can't know where an ingredient came from, there's no obligation to investigate every product you use. Much of the glycerin sold today is plant-based or synthetic.

Some scholars and some Muslims are stricter, especially about pork derivatives, and prefer to avoid doubtful ingredients where they can. Choosing a clearly plant-based toothpaste is a simple way to respect that view. For a similar ingredient question, see Is soap made with animal fat halal to use?

How to find a plant-based toothpaste

Look for "vegetable glycerin", "plant-based glycerin" or "vegan" on the tube.
Check for a halal logo from a body you trust. See How do I know if a halal certificate is real?
Many "natural" and "vegan" toothpastes list the source of glycerin clearly.
Email the manufacturer and ask where the glycerin comes from. Many will tell you.

While fasting

Whatever toothpaste you use, take care not to swallow it during Ramadan, and rinse well. If a little goes down by accident, the fast is not affected. See Can I brush my teeth while fasting?

The sunnah of a clean mouth

The Prophet ﷺ said the siwak is a means of purification for the mouth and pleases the Lord (Sunan an-Nasa'i 5). He also said that if it wouldn't be hard on his community, he would have ordered them to use the siwak for every prayer (Sahih al-Bukhari 887). A miswak has no ingredients at all and is a perfect companion to a toothbrush. See What is a miswak and do I have to use it?

Key points

Glycerin can be plant-based, animal-based or synthetic.
Toothpaste isn't swallowed, and many scholars allow it.
Choose "vegetable glycerin" or a halal label for full peace of mind.
A miswak is a natural, ingredient-free supplement.

Tip: Once you find a plant-based toothpaste you like, buy two or three tubes at a time so you don't have to check labels every week.