The Sages prohibited accepting payment for work done on Shabbat, because this is included in the prohibition on commerce. Even if the “work” is intrinsically permissible on Shabbat (such as guard duty or waiting tables), one may not accept payment for it on Shabbat (BM 58a; SA 306:4). It is also forbidden to accept rent money for anything, whether real estate or objects, that had been rented out on Shabbat (MB 246:3). Even be-di’avad, one may not benefit from money paid for any service rendered on Shabbat (SA 245:6; MB 243:16).
In contrast, payment for work done on Shabbat may be subsumed within weekday payment. For example, an agreement may stipulate that a worker will do guard duty or wait tables for a few hours after Shabbat as well as on Shabbat itself. Even though, in reality, most of the hours were on Shabbat and the payment is primarily for those hours, as long as an agreement was reached before the work started that the employee would also work on Saturday night, the compensation covers the hours worked during the week as well as those on Shabbat. Thus, the Shabbat payment is subsumed within the weekday payment. However, if an agreement was not reached before the work started, then even if the employee did work after Shabbat as well, each workday stands on its own, the payment for Shabbat work cannot be subsumed within the payment for weekday work, and the worker thus may not accept the payment (Ĥayei Adam 60:8; MB 306:21; SSK 28:64-68).
Along the same lines, one may rent out a room for Shabbat, as long as the rental period includes time either on Friday before Shabbat begins or on Saturday night after Shabbat ends. A cab driver can rent out his cab to a non-Jew for Shabbat, as long as the rental period either begins before Shabbat or extends after Shabbat, so that the Shabbat payment can be subsumed within the weekday payment. One may also collect interest on one’s bank account, since the calculations are based on the calendar day and not the times that Shabbat starts and ends. Accordingly, whatever is earned over Shabbat can be seen as subsumed within the weekday earnings of Friday morning and afternoon and Saturday night.
One who immerses in a mikveh on Shabbat may pay the mikveh fee after Shabbat. There are two reasons for this. First, it is for the sake of a mitzva, and second, the payment is not for the immersion itself, but for the cleaning and heating of the mikveh, which started before Shabbat.
One may give a gift on Saturday night to someone who worked voluntarily over Shabbat. Examples include one who set up the synagogue and one who served as a waiter at a Shabbat meal. Since there is no obligation to compensate him at all, whatever is given is not considered payment (Pri Megadim; MB 306:15).
The poskim disagree about whether one may accept payment for serving as a ĥazan or for other mitzva-related jobs undertaken on Shabbat. Some say that even when a job involves a mitzva, one may not accept payment for it. If this is correct, a ĥazan may not be paid for leading the services on Shabbat. Others maintain that one may be paid for a mitzva-related job on Shabbat, but that nothing good will come of this income. In practice, it is proper to stipulate that any payment will also include work performed during the week. For example, a ĥazan will be paid for practicing before he leads the Shabbat services, or for an additional prayer service that he will lead during the week. This way the Shabbat payment can be subsumed within the weekday payment (SA and Rema 306:5).
A doctor who is on call to provide medical care during Shabbat is entitled to demand payment after Shabbat. The reason is that if he cannot assume that he will be paid, he might refuse to provide care in the future (MB 306:24; Minĥat Shabbat 90:19; SSK 28:75).
. If Shabbat is followed by Yom Tov or vice versa, there is an entire calendar day that is sanctified, and yet one is receiving interest then. At first glance this would seem to be forbidden (Minĥat Yitzĥak 9:59; Be-tzel Ha-ĥokhma 3:38). Nevertheless, this too is permissible because interest is not actually paid daily, but rather all the days are calculated together. Accordingly, the interest in this case can be subsumed within the times before and after the holy days (see Menuĥat Ahava 1:10:30 with n. 69, and Yalkut Yosef vol. 2, p. 133). Similarly, MB 306:20 cites an opinion that payment for Shabbat work is subsumed within payment for weekday work even if an agreement was not reached before the work started if it is likely that the work under the agreement will continue during the week.A waiter may not work on Shabbat with the understanding that his employer will in turn work for him in a different capacity, because working for someone is considered payment. However, one may do guard duty on Shabbat for a friend and arrange for this friend to cover his assigned guard duty elsewhere, because guard duty that prevents loss is not considered payment (SA 307:10). Similarly, one may babysit a family on Shabbat with the understanding that the second person will babysit for the first person’s family at some point in the future (SSK 28:59). If it is one’s turn to set up the dining hall and serve the food on Shabbat, he may switch his Shabbat slot for a different slot. Since there is no monetary compensation involved, swapping is not considered payment (SSK 28:61).
As written above, one who immerses in a mikveh on Shabbat may pay after Shabbat because the payment is for the cleaning and heating done before Shabbat begins (Noda Bi-Yehuda, Mahadura Tinyana, OĤ 26; SSK 28:72). One can also be lenient and rent an apartment for Shabbat only, since it can be argued that the rent also covers the cleaning that takes place before Shabbat (SSK 28:70). It is important to know that in a time of need, when a large loss is at stake, one may accept payment for work done on Shabbat (Rema 244:6; BHL s.v. “de-bimkom”).