He broke the fast on several days because of the secret habit
Question

I am a young man in my 20s and I have the problem of the secret habit. In more than one year I have practised the secret habit during the day in Ramadaan. Although I know the ruling, I have not made up those days because I am too lazy. Then when the next Ramadaan comes, I do the same thing. Now that Ramadaan is approaching I have resolved to repent sincerely to Allaah, but what should I do about the past days? I remember that last Ramadaan I practised the secret habit on four days; do I have to make them up? If I have to make them up, can I do it after the holy month? Because I am studying overseas in a non-Muslim country, and fasting will be very difficult because there is no change in the times of classes or the schedule.
Praise be to Allah.Firstly: 
We ask Allaah to accept your repentance and to forgive your sins, and to make you steadfast in obedience and righteousness. 
Deliberately breaking the fast in Ramadaan is a grave sin, because it is neglecting an important obligation that Allaah has enjoined upon His slaves, which He prescribed for us and for those who came before us. If this transgression involves another sin, which is the forbidden secret habit, then the sin is compounded – we ask Allaah to keep us safe and sound. 
We have stated that this habit is haraam and explained that it invalidates the fast in the answer to question no. 40589. 
Secondly: 
You have to make up the days on which you broke the fast. If you cannot do that before Ramadaan, it remains a debt that you owe and you have to make them up after Ramadaan. In order to be on the safe side, you should also offer expiation for each day, which means feeding one poor person half a saa’ of rice or the like. Half a saa’ is equivalent to approximately one and a half kilograms.  
Ibn Qudaamah (may Allaah have mercy on him) said: If a person owes any fasts from Ramadaan, he may delay them so long as the next Ramadaan has not come, because of the report narrated by ‘Aa’ishah who said: I would owe fasts from Ramadaan, and I would not make them up until Sha’baan came. Agreed upon. 
It is not permissible for him to delay making them up until the next Ramadaan comes with no excuse, because ‘Aa’ishah (may Allaah be pleased with her) did not delay it to that extent, and if she could she would have done so. 
If he delays it until after the following Ramadaan, then it depends. If it was due to a (valid) excuse, then he does not have to do anything but make up the missed fast, but if it is without an excuse, then in addition to making it up, he has to feed one poor person for each day. This is the view of Ibn ‘Abbaas, Ibn ‘Umar, Abu Hurayrah, Mujaahid, Sa’eed ibn Jubayr, Maalik, al-Thawri, al-Awzaa’i, al-Shaafa’i and Ishaaq. 
Al-Hasan, al-Nakha’i and Abu Haneefah said: He does not have to offer the fidyah, because it was an obligatory fast, and no expiation is required for delaying it, as is also the case if he delays fulfilling a vow. End quote. 
From al-Mughni (3/40). 
This expiation does not increase as the years pass, so if a person delays making up missed Ramadaan fasts for many years with no excuse, he only has to offer one expiation for each day. 
And Allaah knows best.