Fidyah is payable if one cannot observe fasting during or after the Holy month of Ramadan; be it due to poor health, pregnancy or health issues where fasting would prove detrimental to their well-being. The contributory fidyah then goes towards feeding someone in need.
Kaffarah is a form of levy payable if you intentionally break or miss a fast during the month of Ramadan. Should you have a legitimate and unavoidable reason for doing so, it is highly likely this will fall into the fidyah category nevertheless. The forfeit entails either feeding a total of 60 people in need or continuously fasting for 60 days for each fast missed or broken.
The rate at which both fidyah and kaffarah are paid amounts to £4 per person. For example, for each intentionally missed fast, you would be required to pay £4 per person for 60 people, which amounts to £240 in kaffarah.
So to conclude, zakat, fidyah and kaffarah are all deemed obligatory, whereas sadaqah (charity) is a selfless and humble act of sincerity which is carried out without even being obligated to do so.