Day to day Halachot regarding Ribis

Hi, I would like to know with regard to ribis, when I borrow half a cup of oil from my neighbor, do I need to measure how much I received in order to return the exact amount?"

Thank you for your question.

Ribbis De’rabannan:

The biblical prohibition of Ribis is, that at the time of lending money, the borrower must not condition the loan on receiving more than what was originally lent out.

However, the rabbis added a prohibition, that even if there was no condition to return more than what was lent, the borrower may not give back more than what he received, either as a present or in recognition of the favor that the lender did for him.

שולחן ערוך יורה דעה הלכות ריבית סימן ק”ס

סעיף ד

אפילו אם הלוה נותן לו יותר, מדעתו, בשעת הפרעון, שלא התנה עמו, ואינו אומר שנותנו לו יותר בשביל רבית, אסור.

....אבל אם נהנה ממנו מדעתו, מותר בדבר שהיה עושה לו אף אם לא הלווהו. ובלבד שלא יהא דבר של פרהסיא, כגון לדור בחצרו ולהשתמש בעבדיו.

Shulchan Aruch, Yoreh Deah, Laws of Interest, Siman 160. Seif 4:

Even if the borrower gives extra, willingly, at the time of repayment, without any prior agreement, and he does not state that he is giving more due to interest, it is forbidden. ...However, if he benefits from him (the borrower) willingly, it is permitted in a case that he (the borrower) would have done it for him anyway, even if he had not lent him any money, as long as it is not something done publicly, such as living in his courtyard or using his servants.

We see from this halacha that even if there was no agreed condition to return the extra amount, it is nevertheless prohibited.

The Rema writes in Siman 162, Seif 1 that if the amount is negligible and it's not an amount that people pay attention to, then one doesn't have to ensure that the amount being returned is the exact amount received. This is because such an amount is not considered by people to be significant. This halacha is also based on the Rashba, Tractate Shabbos, page 148b, where it is stated that an amount that people generally disregard is not considered Ribbis.

In practice

An amount that does not have a known weight for example

1. Half a cup of coffee

2. Half a cup of sugar

3. Fruits and vegetables that are hard to assess their weight

These are cases of things that do not require one to be exact with the amount of food he is returning, since the extra amount is not recognizable.

However, if someone borrowed half a bottle of milk, they cannot return a full bottle. It is even prohibited to return a “full small bottle” even if it contains the same amount as what was borrowed, since a “full small bottle” generally costs more than a half-full bottle.
If one feels awkward returning a half-full bottle, it is permitted to explain to the neighbor that they would have liked to return a full bottle, but since it would have been considered ribbis, that is why they are returning only half a bottle. (Saying this does not constitute ‘Ribbis Devarim’ since the intention for explaining this to the neighbor is because they feel awkward, and not to honor the neighbor in return for the favor).

Same too, let's say a person borrowed from his neighbor a pack of medium-sized eggs and now wants to return a pack of large-sized eggs; this would be prohibited. since it is an obvious change from the amount originally borrowed. However, if he did not borrow a pack of eggs but a few medium-sized eggs and now wants to return a few Large-sized eggs, then it would be permitted for two reasons.

1. Since it’s only a few eggs, not a pack, we can say that it’s a small unrecognizable amount.

2. One isn't obliged to buy especially medium-sized eggs to be able to return some to his neighbor when he normally uses large-sized eggs. The reason being that his intention of returning the large-sized eggs is not because he wants to benefit his neighbor, but rather because that is the type of eggs that he uses. Therefore, since it’s a small amount, we do not oblige him to buy medium-sized eggs just to return some to his neighbor.

Wishing you well.

Shulchan Aruch, Yoreh Deah, Hilchot Ribit, Siman 160, Seif 4

Rema, Siman 162, Seif 1

Rashba, Tractate Shabbos, page 148b