What is Apportionment?

Legal Definition
The legal term apportionment (French apportionement; Med. Latin apportionamentum; derived from Latin portio, share) means distribution or allotment in proper shares.

It is a term used in law in a variety of senses. Sometimes it is employed roughly and has no technical meaning; this indicates the distribution of a benefit (e.g. salvage or damages under the Fatal Accidents Act 1846, ยง 2), or liability (e.g. general average contributions, or tithe rent-charge), or the incidence of a duty (e.g. obligations as to the maintenance of highways).

In its strict legal interpretation apportionment falls into two classes: "apportionment in respect of estate" and "apportionment in respect of time."
-- Wikipedia
Legal Definition
Contracts. Lord Coke defines it to be a division or partition of a rent, common, or the like, or the making it into parts. Co . Litt. 147. This definition seems incomplete. Apportionment frequently denotes, not, division, but distribution; and in its ordinary technical sense, the distribution of one subject in proportion to another previously distributed. 1 Swanst. C. 87, n.

2. Apportionment will here be considered only in relation to contracts, by talking a view, 1, of such as are purely personal and, 2, of such as relate to the realty.

3. – 1. When a Purely personal contract is entire and not divisible in its nature, it is manifest it cannot be apportioned; as when the subject of the contract is but one thing, and there is but one creditor and one debtor, neither can apportion the obligation without the consent of the other. In such case the creditor cannot force his debtor to pay him a part of his debt only, and leave the other part unpaid, nor can the debtor compel his creditor to receive a part only of what is due to him on account of his claim. Nor can the assignee of a part sustain an action for such part. 5 N. S. 192.

4. When there is a special contract between the parties, in general no compensation can be received unless the whole contract has been actually fulfilled. 4 Greenl. 454; 2 Pick. R. 267; 10 Pick. R. 209; 4 Pick. R. 103; 4 M'Cord, R. 26, 246; 6 Verm. R. 35. The subject of the contract being a complex event, constituted by the performance of various acts, the imperfect completion of the event, by the performance of only some of those acts, cannot, by virtue of that contract, of which it is not the subject, afford a title to the whole, or any part of the stipulated benefit. See 1 Swanst. C. 338, n. and the cases there cited; Story, Bailm. 441; Chit. Contr. 168; 3 Watts, 331; 2 Mass. 147, 436; 3 Hen. & Munf. 407; 2 John. Cas. 17; 13 John. R. 365; 11 Wend. 257; 7 Cowen, 184; 8 Cowen, 84; 2 Pick. 332. See generally on the subject of the apportionment, of personal obligations, 16 Vin. Ab. 138; 22 Vin. Ab. 13; Stark. Ev. part 4, p. 1622; Com. Dig. Chancery, 2 E and 4 N 5; 3 Chit. Com. Law 129; Newl. Contr. 159; Long on Sales, 108. And for the doctrine of the civil law, see Dumoulin, de dividuo et individuo, part 2, n. 6, 7; Toull. Dr. Civ. Fr. liv. 3, tit 3, c. 4, n. 750, et seq.

5. – 2. With regard to rents, the law is different. Rents may in general be apportioned, and this may take place in several ways; first, by the act of the landlord or reversioner alone, and secondly, by virtue of the statute of 11 Geo. II., c. 19, s. 15, or by statutes in the several states in which its principles have been embodied.

6. – 1. When there is a subsisting obligation on the part of the tenant to pay a certain reat, the reversioner may sell his estate in different parts, to as many persons as he may deem proper, and the lessee or tenant will be bound to pay to each a proportion of the rent. 3 Watts, 404; 3 Kent Com. 470, 3d. ed.; Co. Litt. 158 a; Gilb. on Rents, 173; 7 Car. 23; 13 Co. 57 Cro. Eliz. 637, 651; Archb. L. &. T. 172 5 B. & A.876; 6 Halst. 262. It is usual for the owners of the reversion to agree among themselves as to the amount which each is to receive; but when there is no agreement, the rent will be apportioned by the jury. 3 Kent, Com. 470; 1 Bouv. Inst. n. 697.

7. – 2. Rent may be apportioned as to time by virtue of the stat. 11 Geo. H., C. 19, s. 15, by which it is provided that the rent due by a tenant for life, who dies during the currency of a quarter, of a year, or other division of time at which the rent was made payable, shall be apportioned to the day of his death. In Delaware, Missouri, New Jersey, and New York, it is provided by statutes, that if the tenant for life, lessor, die on the rent day, his executors may recover the whole rent; if before, a proportional part. In Delaware, Kentucky, Missouri, and New York, when one is entitled to rents, depending on the life of another, he may recover them notwithstanding the death of the latter. In Delaware, Kentucky, Missouri, and Virginia, it is specially provided, that the husband, after the death of his wife, may recover the rents of her lands. 1 Hill. Ab. c. 16, 50. In Kentucky, the rent is to be apportioned when the lease is determined upon any contingency.

8. When the tenant is deprived of the land, as by eviction, by title paramount, or by quitting the premises with the landlord's consent, in the absence of any agreement to the contrary, his obligation to pay rent ceases, as regards the current quarter or half year, or other day of payment, as the case may be. But rent which is due may be recovered. Gilb. on Rents, 145; 3 Kent, Comm. 376; 4 Wend. 423; 8 Cowen, 727 1 Har. & Gill, 308; 11 Mass. 493. See 4 Cruise's Dig. 206; 3 Call's R. 268; 4 M'Cord 447; 1 Bailey's R. 469; 2 Bouv. Inst. n. 1675, et seq.
-- Bouviers Law Dictionary
Legal Definition
The division, partition or distribution of a subject-matter in proportionate parts. Co. Litt. 147; 1 Swanst. 37, n.; 1 Story, Eq. Jut. 475a.

Of contracts. The allowance, in case of a severable contract, partially performed, of a part of the entire consideration proportioned to the degree in which the contract was carried out Of rent. The allotment of their shares in a rent to each of several parties owning it. The determination of the amount of rent to be paid when the tenancy is terminated at some period other than one of the regular intervala for the payment of rent Swint v. McCalmont Oil Co., 184 Pa. 202, 38 Atl. 1021, 63 Am. St Rep. 791; Gluck v. Baltimore, 81 Md. 315, 32 Atl. 515, 48 Am. St. Rep. 515.

Of incumbrances. Where several persons are interested in an estate, apportionment, as between them, is the determination of the respective amounts which they shall contribute towards the removal of the incumbrance.

Of corporate shares. The pro tanto division among the subscribers of the shares allowed to be issued by the charter, where more than the limited number have been subscribed for. Clarke v. Brooklyn Bank, 1 Edw. Ch. (N. Y.) 368; Haight v. Day, 1 Johns. Ch. (N. Y.) 18.

Of common. A division of the right of common between several persons, among whom the land to which, as an entirety, it first bslonged has been divided. Of representatives. The determination upon each decennial census of the number of representatives In congress which each state shall elect, the calculation being based upon the population. See Const U. S. art. 1, i 2. Of taxes. The apportionment of a tax consists in a selection of the subjects to be taxed, and in laying down the rule by which to measure the contribution which each of these subjects shall make to the tax. Barfield v. Gleason, 111 Ky. 491, 63 S. W. 964.
-- Black's Law Dictionary
Legal Definition
Partition into shares.
-- Ballentine's Law Dictionary