Are women obligated in tashlumin?

If one unintentionally failed to daven, he must do tashlumin (make it up) during the next tefilla. Tashlumin applies regardless of whether he failed to daven due to forgetting, a mistaken halachic ruling, circumstances beyond his control, or poor time management. A woman who regularly davens should also keep the halachos of tashlumin. For Ma’ariv, however, there is no tashlumin for a woman, even if she regularly davens Ma’ariv. A child who is the age of chinuch should be taught to do tashlumin if he misses a tefilla. A chazan can be yotzei his obligation of tashlumin with his recital of Chazoras Hashatz.

סי' ק"ח ס"א ס"ק א' ד' ביה"ל ד"ה טעה ביאורים ומוספים דרשו 3

When is one obligated to daven for a third time?

The make-up Shemoneh Esrei is davened after the obligatory Shemoneh Esrei of the next tefilla. The first Shemoneh Esrei must be for the obligation and the second tefilla for the make-up. If it is clearly apparent that the order was reversed, one is not yotzei his obligation for tashlumin and he will have to daven for a third time. An example could arise in the case of a person who omitted Mincha on Shabbos and needs to daven Ma’ariv twice. If he adds the Havdalah passage to the second tefilla and not the first, he is demonstrating that the first tefilla was intended as the make-up for his Shabbos davening and the second one was meant to fulfill his present obligation.  Since the mix-up was apparent, he must daven again. If one intended for the first tefilla to be his make-up and the second one to fulfill his present obligation but the mix-up was not apparent, the poskim disagree about whether he is yotzei his obligation of tashlumin. The halacha follows the view which holds that one does not fulfill his obligation and he must daven a third time. In deference to the other view, one should have in mind that if he is not obligated, his third tefilla should be a nedavah. On Shabbos he should not include this stipulation.

ס"א ס"ק ו'-ז' ביאורים ומוספים דרשו 15

Is it ever necessary to daven Shemoneh Esrei four times?

In a case where a person intended his first tefilla to be for the present obligation, but he made a critical omission which required him to repeat Shemoneh Esrei, the poskim discuss whether he must repeat his tashlumin as well.  A minority view maintains that doing so is necessary; since his first Shemoneh Esrei was not valid, his tashlumin turned into the first tefilla and thereby also became invalid. Most poskim disagree and hold that the first Shemoneh Esrei still counts as a tefilla and the tashlumin retains its status as the second tefilla. In a case where one davened both tefillos without specific intention, he can change his second tefilla (if he did not make any omissions) into his obligatory tefilla and use the third one as the tashlumin. Doing so satisfies all opinions.

ס"ק ט' 

• A person who is not sure whether he already davened should daven. Before he begins, he should stipulate the following: If I have already davened, this tefilla should be a nedavah (a voluntary offering), and if I have not yet davened, this tefilla should be the obligatory tefilla.

• Since tefilla was instituted as a replacement for korbonos, there is no option to daven multiple obligatory tefillos. However, since an individual may offer multiple korbonos nedavah, one who already davened may choose to daven additional tefillos nedavah. 

• When one davens a tefillas nedavah, he must incorporate a new request. Doing so makes it clear that the tefilla is a nedavah and not a repeat of the chovah. The request must be incorporated into one of the middle brochos and must be a request for the fulfillment of a new need which he was not aware of when he davened (possibly) the previous time.

• What is the proper way to separate the obligatory Shemoneh Esrei from the tashlumin?

• Can there be a break between the obligatory Shemoneh Esrei and the tashlumin?

• Can a person who wakes up from a coma make up all the tefillos he missed?