What is the ruling on making up missed fast-days by fasting one or two days every week?

During menstruation and post-natal bleeding, women are legally obligated to refrain from fasting. Scholars have agreed that it is prohibited for menstruating women or women in post natal bleeding to fast and that, if they do, their fast is invalid. They have also unanimously agreed that breaking a fast due to menstruation necessitates making up the missed fastdays only.

Making up the missed fast days
It is not obligatory to make up the missed fast-days immediately after Ramadan if there was a valid excuse for breaking the fast. Rather, the matter is open and a person may make up his missed fast days anytime during the upcoming year before the next Ramadan.

Evidence from Sunnah
In an authentic report recorded by Muslim, Aisha said that she used to make up her missed fast-days in the month of Sha’ban.

Scholarly opinions
A woman who fails to make up her missed fast-days before the next Ramadan is to fast the current Ramadan and make up her missed fasts afterwards.
- Hanafi scholars and Al-Hassan Al-Basri maintained that a woman who fails to make up her missed fasts before the next Ramadan is not required to pay fidya [compensation] whether or not she had an excuse for this delay.
- Imams Malik, Al-Shafi'i and Ahmed maintained that it is obligatory for a woman to make up her missed fasts if she had an excuse for the delay. Otherwise, she must pay a fidya in addition to making up her missed fasts. This is the opinion we advocate.
It is not a condition to make up the missed fast-days of Ramadan consecutively. The Prophet (peace and blessings be upon him) said: "He can make them up either separately or consecutively, however he wishes" [Al-Daraqutni].

The ruling
It is obligatory for the inquirer to hasten to make up the accumulated missed fasts before the arrival of next Ramadan.

And God the Almighty knows best.