Driving from Idaho to Montana

The drive from central Idaho (e.g., Boise) to central Montana (e.g., Helena) is roughly 310 miles (500 km) and takes about 5 hours via I-84 east to I-86 east to I-15 north. Distances vary significantly depending on specific start/end points—Idaho and Montana share a long border (e.g., Coeur d'Alene to Missoula is ~170 miles / 3 hrs; Idaho Falls to West Yellowstone is ~110 miles / 2 hrs). Mountain weather can affect travel, especially winter.