Update only modifies the *first* document it finds by default. You can set an option to modify *all* matched documents demo->products; $c->drop(); $c->insert( [ '_id' => 'blue-elephpant', 'generation' => 1, 'price' => 7.5 ] ); $c->insert( [ '_id' => 'pink-elephpant', 'generation' => 2, 'price' => 8.0 ] ); $c->insert( [ '_id' => 'green-elephpant', 'generation' => 3, 'price' => 7.5 ] ); $c->update( [ 'generation' => [ '$lte' => 2 ] ], // criteria [ '$inc' => [ 'price' => -2.0 ] ], // update spec [ 'multiple' => true ] // options: multiple ); ?>]]>