A closing cap for a container , comprising a lateral wall extending around an axis (Z) 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 (Z) 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 (Z) 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 (Z) 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 (Z) 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 (Z) 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. <EOS>