Yes, in most cases it is safe to leave butter out overnight, especially if it is salted and your kitchen is reasonably cool. Always check it before using: if it smells sour, tastes off, or has visible mold, throw it away.

Basic safety

• Salted butter is low in moisture and relatively high in fat, which makes it less friendly to most harmful bacteria compared with many other dairy products.
• The biggest risk from leaving butter out is that it can turn rancid (develop an unpleasant flavor and smell) rather than becoming acutely dangerous to eat.

Time and temperature

• In a typical cool kitchen, many food safety sources consider salted butter left out overnight (up to about a day) generally acceptable for home use.
• In a very warm room (for example, consistently above about 75–80°F/24–27°C), butter softens more, spoils faster, and is better kept in the fridge when you are not actively using it.

Salted vs. unsalted

• Salted butter keeps better at room temperature because salt acts as a mild preservative.
• Unsalted butter is more perishable and is best left out only for a few hours to soften, then returned to the refrigerator.

How to leave it out more safely

• Use a clean, covered butter dish to protect it from dust, insects, and other kitchen contaminants.
• Keep the dish away from direct sunlight, the stove, or other heat sources, and only leave out the amount you plan to use within a day or so.

When to throw it away

• Discard the butter if you notice a strong, paint-like or sour smell, visible mold, or a strange color.
• If you are immunocompromised, pregnant, very young, or elderly, it is safer to be more cautious and keep butter refrigerated when not in use.