The highway runs from Claremont, at the Vermont border on the Connecticut River, to Hopkinton, west of Concord.

The western terminus of NH 103 is in Claremont at the New Hampshire–Vermont state line on the Connecticut River, running concurrently with New Hampshire Route 12.

Northwest of Hopkinton, the road runs merged with New Hampshire Route 127 for a distance of 2.127 miles (3.423 km).

NH 103A runs down the entire length of the east side of Lake Sunapee and provides access to the local roads along the lakeshore.

The northern terminus is at New Hampshire Route 11, Newport Road, at the north end of the lake near Interstate 89.