How much does a Bechor inherit?
A firstborn son, who is Halachically defined as a Bechor, inherits a double share from amongst certain assets of his father. For example, if a father passed away leaving five sons, and one is a Halachically valid firstborn, the firstborn receives 1/3 [33%] of the assets, while each of the other four brothers receives a 1/6 [17%] of the assets. If the father left nine sons, the firstborn brother takes a 1/5 [20%] of the assets while each of the eight remaining sons takes a 1/10 [10%] of the assets. This method of distribution is to be followed in all cases. [Accordingly, one splits the assets by one more than the current number of children, and the Halachic firstborn receives two of those portions. For example, if there are 5 children, one splits the assets into six portions, and the first born takes two out of the six portions. So if the father left $100,000 of tangible assets for the five sons, the eldest son receives $33,000, while each of the 4 sons receive close to $16,500.]
Mother’s assets: A first born son only inherits a double portion from the assets of his father, and not from the assets of his mother. This applies even if he is the firstborn son of his father and mother, nonetheless, he receives an equal portion from his mother’s assets, just as all the other brothers.
 Michaber C.M. 277:1; Rambam Nechalos 2:1; Bava Basra 122b
 See 277 regarding who is defined as a Bechor and who is excluded.
 See 278 that only tangible assets that are currently in the hands of the father receive a double portion inheritance. A major exception of the above would be a bank account, which is excluded from the double portion being it is not tangible assets and is viewed as owed funds.
 The ruling here comes to negate an erroneous understanding of the “double portion”, which interprets it to mean that the first born receives twice the amount of all the other sons put together. Rather, the first born is viewed as if he is two sons, and receives two portions, each one being equal to the single portion of each son, individually.
 Smeh 277:2
 Michaber C.M. 278:1; Bechoros 51b
 The reason: This is learned from the verse which states “Ki Lo Mishpat Habechora,” which means that the status of a Bechor applies to [the assets of] a man and not to [the assets of] a woman. [Smeh 278:1; Bechoros ibid]