The source of the River Calder is located on the Pennines in Calderdale, West Yorkshire. The initial waters rise to the west of the village of Lydgate, which lies inbetween the village of Cornholme (to the northwest) and the town of Todmorden (to the southeast).
The river initially flows southeast, running virtually alongside the A646 road until it reaches Todmorden, where it meets its tributary, Walsden Water. The Calder then flows in an easterly direction through the town, running practically parallel to the Rochdale Canal, which will accompany the river as far as Sowerby Bridge, near the city of Halifax.
Downstream of Todmorden the river heads northeast, passing through the hamlets of Eastwood and Charlestown, it then heads east through Stubbing Holme and on to the town of Hebden Bridge, where it meets another tributary, the River Hebden.
As the Calder leaves Hebden Bridge, it passes under the Rochdale Canal and heads southeast to the small town of Mytholmroyd. It winds its way through the town and then heads east for just over half a mile, after which the river starts to head southeast with the village of Luddendenfoot on its west bank, and the village of Luddenden on the eastern bank.
The town of Sowerby Bridge is next on the banks, where the River Calder meets another of its tributaries, the River Ryburn. After its confluence with the River Ryburn the Calder heads east for about a mile, it then winds its way southeast passing the villages of Copley and Greetland, then on to the market town of Elland.
As the River Calder reaches Elland it begins to head northeast, it flows across the northern edge of the town past the Lowfields Business Park and continues northeast until it reaches the village of Brookfoot. At Brookfoot the Calder once again heads southeast, flowing between the villages of Brighouse, which lies on the eastern bank, and Rastrick on its western bank.
Maintaining its southeastern course, the Calder flows under the M62 motorway and onto the district of Bradley. At Bradley the Calder absorbs another tributary, the River Colne, after which it heads northeast for about half a mile, before turning southeast to flow down the western flank of the town of Mirfield.
As the river reaches the village of Upper Hopton it changes direction once again, this time heading northeast, passing the Ravensthorpe Industrial Estate and into the town of Dewsbury. The Calder flows through the southern part of the town, then heads southeast flowing between the village of Thornhill which lies on its western bank, and the market town of Ossett on the eastern bank.
The River Calder maintains its southeasterly course, passing near the village of Middlestown, and flowing down the western flank of the large village of Horbury before heading northeast once again. The next major settlement on the banks of the Calder is the town of Wakefield, which sits on the northern bank of the river.
Downstream of Wakefield the Calder heads southeast for about half a mile, then heads east northeast with the small village of Agbrigg sitting on its southern bank. The river then snakes its way northeast passing the small village of Kirkthorpe, after which the river heads north for about half a mile before winding its way northwest and on to the village of Stanley.
Leaving Stanley behind the river meanders its way east northeast, flowing between the villages of Bottom Boat and Altofts. The Calder then passes under the M62 motorway and flows past the Normanton Industrial Estate, which sits on the southern bank, and the village of Methley, which sits just north of the river.
The river continues east northeast, passing the Whitwood Mere area of Castleford and meeting its confluence with the River Aire
, just north of the town of Castleford.