The C403 starts at the Longforgan Junction on the A90, and initially follows the dual carriageway south west. This is a new access road built to remove one of the many central reservation gaps that were percieved to be a major accident problem on the A90. After perhaps half a mile, the C403 finds its original start point, and turns north then north west as it climbs up into the Sidlaw Hills. Near the north end, the road is briefly the council boundary, but the modern boundary turns away, just before the end of the route on the A923 at Tullybaccart.
Heading eastwards along the west end of Knapp Den.