A closing cap for a container, comprising a lateral wall extending around an axis and a transversal wall positioned at one end of the lateral wall, a separating line being provided on the lateral wall to define: a retaining ring, which is configured to remain anchored to a neck of the container and extends as far as a free edge, and a closing element removably engageable with the neck, so as to open or close the container; wherein the separating line extends around the axis and is circumferentially interrupted to define in the lateral wall a joining zone, which extends for a first angle (α), in which the retaining ring and the closing element are joined; wherein the retaining ring comprises: an engagement element which projects inwards from the free edge and is configured to engage with a locking ring of the neck, the engagement element being in a bent configuration when the cap is in the closed condition; characterized in that the the retaining ring further comprises: a first incision line and a second incision line, which are transversal to the axis and are positioned circumferentially at the sides of a connecting portion, which is positioned at least in the joining zone and extends for a second angle (β); the first incision line and the second incision line being configured to allow deformability at least of the connecting portion and of a region of the engagement element, which extends at least in the second angle (β), so that in a final step of a first opening of the closing element, the region of the engagement element goes beyond the locking ring and can deform, being positioned resting on the locking ring in an extended configuration. a retaining ring, which is configured to remain anchored to a neck of the container and extends as far as a free edge, and a closing element removably engageable with the neck, so as to open or close the container; wherein the separating line extends around the axis and is circumferentially interrupted to define in the lateral wall a joining zone, which extends for a first angle (α), in which the retaining ring and the closing element are joined; wherein the retaining ring comprises: an engagement element which projects inwards from the free edge and is configured to engage with a locking ring of the neck, the engagement element being in a bent configuration when the cap is in the closed condition; characterized in that the the retaining ring further comprises: a first incision line and a second incision line, which are transversal to the axis and are positioned circumferentially at the sides of a connecting portion, which is positioned at least in the joining zone and extends for a second angle (β); the first incision line and the second incision line being configured to allow deformability at least of the connecting portion and of a region of the engagement element, which extends at least in the second angle (β), so that in a final step of a first opening of the closing element, the region of the engagement element goes beyond the locking ring and can deform, being positioned resting on the locking ring in an extended configuration. a first incision line and a second incision line, which are transversal to the axis and are positioned circumferentially at the sides of a connecting portion, which is positioned at least in the joining zone and extends for a second angle (β); the first incision line and the second incision line being configured to allow deformability at least of the connecting portion and of a region of the engagement element, which extends at least in the second angle (β), so that in a final step of a first opening of the closing element, the region of the engagement element goes beyond the locking ring and can deform, being positioned resting on the locking ring in an extended configuration.