When someone cannot fast in Ramadhaan and can’t make up the lost days afterwards (for example, due to ill health or pregnancy), then they should pay for a poor person to be fed. This is known as fidyah.
The present rate is £5 for each day that is missed. (This should provide one person with two meals or two people with one meal.) If someone misses all the fasts of Ramadan, it would amount to £150.