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, a 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 a first cutting edge extending along an intersection between the first surface and the circumferential surface, and a second cutting edge extending along an intersection between the second surface and the circumferential surface, the first and second cutting edges (20, 20′′′), as seen in a view towards the first and second surfaces (14, 16) respectively, extending along a corner of the cutting insert, wherein the first cutting edge comprises a first main cutting edge, a first corner cutting edge, and a first surface-wiping secondary cutting edge, wherein the first main cutting edge adjoins to the first corner cutting edge, and the first corner cutting edge adjoins to the first surface-wiping secondary cutting edge, wherein the second cutting edge comprises a second main cutting edge, a second corner cutting edge, and a second surface-wiping secondary cutting edge, wherein the second main cutting edge adjoins to the second corner cutting edge, and the second corner cutting edge adjoins to the second surface-wiping secondary cutting edge, wherein the circumferential surface comprises a countersunk circumferential waist portion situated at the median plane, and wherein the first main cutting edge is arranged on an opposite side of the countersunk circumferential waist portion to the second surface-wiping secondary cutting edge, and the first surface-wiping secondary cutting edge is arranged on an opposite side of the countersunk circumferential waist portion to the second main cutting edge, wherein the circumferential surface comprises a first clearance surface extending along the first main cutting edge, the first clearance surface extending at an acute angle (c) to the median plane along the first main cutting edge (24, 24'), such that the first clearance surface is forming a negative nominal clearance angle (α), wherein the circumferential surface comprises a second clearance surface extending along the second main cutting edge, the second clearance surface extending at an acute angle (c) to the median plane along the second main cutting edge, such that the second clearance surface is forming a negative nominal clearance angle (α), characterized in that the first main cutting edge is arranged inside the countersunk circumferential waist portion, as seen in the view towards the first surface, and wherein the second main cutting edge is arranged inside the countersunk circumferential waist portion, as seen in the view towards the second surface. the cutting insert comprises a first cutting edge extending along an intersection between the first surface and the circumferential surface, and a second cutting edge extending along an intersection between the second surface and the circumferential surface, the first and second cutting edges (20, 20′′′), as seen in a view towards the first and second surfaces (14, 16) respectively, extending along a corner of the cutting insert, wherein the first cutting edge comprises a first main cutting edge, a first corner cutting edge, and a first surface-wiping secondary cutting edge, wherein the first main cutting edge adjoins to the first corner cutting edge, and the first corner cutting edge adjoins to the first surface-wiping secondary cutting edge, wherein the second cutting edge comprises a second main cutting edge, a second corner cutting edge, and a second surface-wiping secondary cutting edge, wherein the second main cutting edge adjoins to the second corner cutting edge, and the second corner cutting edge adjoins to the second surface-wiping secondary cutting edge, wherein the circumferential surface comprises a countersunk circumferential waist portion situated at the median plane, and wherein the first main cutting edge is arranged on an opposite side of the countersunk circumferential waist portion to the second surface-wiping secondary cutting edge, and the first surface-wiping secondary cutting edge is arranged on an opposite side of the countersunk circumferential waist portion to the second main cutting edge, wherein the circumferential surface comprises a first clearance surface extending along the first main cutting edge, the first clearance surface extending at an acute angle (c) to the median plane along the first main cutting edge (24, 24'), such that the first clearance surface is forming a negative nominal clearance angle (α), wherein the circumferential surface comprises a second clearance surface extending along the second main cutting edge, the second clearance surface extending at an acute angle (c) to the median plane along the second main cutting edge, such that the second clearance surface is forming a negative nominal clearance angle (α), characterized in that the first main cutting edge is arranged inside the countersunk circumferential waist portion, as seen in the view towards the first surface, and wherein the second main cutting edge is arranged inside the countersunk circumferential waist portion, as seen in the view towards the second surface.