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 separation 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; - a closing element removably engageable with the neck, so as to open or close the container; wherein - the separation line extends about the axis and is circumferentially interrupted to form 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 cap comprises - a tab, made in the joining zone, which extends circumferentially for a second angle (β) and is connected to the joining zone; characterized in that the retaining ring comprises: - a retaining portion and a free portion, wherein the retaining portion comprises an engagement element configured to engage internally with a locking ring of the neck during a passage from a closed condition to an open condition of the closing element, and wherein the free portion comprises a movement element which extends circumferentially at least in the second angle (β) and is configured, during said passage, to allow a movement of the free portion along an axis parallel to the axis; - wherein the tab is connected to the joining zone by a hinge zone, about which the tab may optionally bend and comprises a bottom edge, which is positioned on the opposite side relative to the hinge zone and is interposed between the hinge zone and the free edge of the retaining ring, and a pair of lateral edges, which extend from the hinge zone, the lateral edges being transversal to the bottom edge; - wherein the tab comprises an outer part, made in the retaining ring and an inner part, made in the closing element, which are separated respectively from the retaining ring and from the closing element by respective stretches of the lateral edges. - a retaining ring, which is configured to remain anchored to a neck of the container and extends as far as a free edge; - a closing element removably engageable with the neck, so as to open or close the container; wherein - the separation line extends about the axis and is circumferentially interrupted to form 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 cap comprises - a tab, made in the joining zone, which extends circumferentially for a second angle (β) and is connected to the joining zone; characterized in that the retaining ring comprises: - a retaining portion and a free portion, wherein the retaining portion comprises an engagement element configured to engage internally with a locking ring of the neck during a passage from a closed condition to an open condition of the closing element, and wherein the free portion comprises a movement element which extends circumferentially at least in the second angle (β) and is configured, during said passage, to allow a movement of the free portion along an axis parallel to the axis; - wherein the tab is connected to the joining zone by a hinge zone, about which the tab may optionally bend and comprises a bottom edge, which is positioned on the opposite side relative to the hinge zone and is interposed between the hinge zone and the free edge of the retaining ring, and a pair of lateral edges, which extend from the hinge zone, the lateral edges being transversal to the bottom edge; - wherein the tab comprises an outer part, made in the retaining ring and an inner part, made in the closing element, which are separated respectively from the retaining ring and from the closing element by respective stretches of the lateral edges.