A cutting insert for a shoulder milling tool, the cutting insert having a trigonal shape and a median plane extending through the cutting insert, the cutting insert comprising a first surface, an opposite second surface, and a circumferential surface extending between the first surface and the second surface, the first and second surfaces (14, 16) extending on opposite sides of the median plane, wherein the cutting insert comprises three indexable cutting edges (20, 20', 20") extending along an intersection between the first surface and the circumferential surface, wherein each indexable cutting edge, as seen in a view towards the first surface, is extending along a corner of the trigonally shaped cutting insert, wherein each indexable cutting edge (20, 20', 20") comprises a main cutting edge, a corner cutting edge, and a surface-wiping secondary cutting edge, wherein the main cutting edge adjoins to the corner cutting edge, and the corner cutting edge adjoins to the surface-wiping secondary cutting edge, characterised in that the surface-wiping secondary cutting edge is inclined in relation to the median plane such that the distance to the median plane decreases in a direction towards the corner cutting edge, wherein the circumferential surface comprises a clearance surface extending along the main cutting edge, wherein the clearance surface along the main cutting edge extends at an acute angle (c) to the median plane, such that the clearance surface is forming a negative nominal clearance angle (α), wherein the circumferential surface comprises a first abutment surface configured for abutment against an axial and/or radial support surface of the shoulder milling tool, the first abutment surface extending along at least part of the main cutting edge, and wherein the circumferential surface comprises a second abutment surface configured for abutment against an axial and/or radial support surface (80, 82) of the shoulder milling tool, the second abutment surface extending along at least a part of the surface-wiping secondary edge, and wherein the first surface comprises a flat centre surface transforming into an inclined main rake face adjacent to the main cutting edge, wherein the entire main cutting edge and the inclined main rake face extends at a greater distance from the median plane than the flat centre surface. the cutting insert comprises three indexable cutting edges (20, 20', 20") extending along an intersection between the first surface and the circumferential surface, wherein each indexable cutting edge, as seen in a view towards the first surface, is extending along a corner of the trigonally shaped cutting insert, wherein each indexable cutting edge (20, 20', 20") comprises a main cutting edge, a corner cutting edge, and a surface-wiping secondary cutting edge, wherein the main cutting edge adjoins to the corner cutting edge, and the corner cutting edge adjoins to the surface-wiping secondary cutting edge, characterised in that the surface-wiping secondary cutting edge is inclined in relation to the median plane such that the distance to the median plane decreases in a direction towards the corner cutting edge, wherein the circumferential surface comprises a clearance surface extending along the main cutting edge, wherein the clearance surface along the main cutting edge extends at an acute angle (c) to the median plane, such that the clearance surface is forming a negative nominal clearance angle (α), wherein the circumferential surface comprises a first abutment surface configured for abutment against an axial and/or radial support surface of the shoulder milling tool, the first abutment surface extending along at least part of the main cutting edge, and wherein the circumferential surface comprises a second abutment surface configured for abutment against an axial and/or radial support surface (80, 82) of the shoulder milling tool, the second abutment surface extending along at least a part of the surface-wiping secondary edge, and wherein the first surface comprises a flat centre surface transforming into an inclined main rake face adjacent to the main cutting edge, wherein the entire main cutting edge and the inclined main rake face extends at a greater distance from the median plane than the flat centre surface.