This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
A mistake as to the amount due on a debt,1 even where the facts as to the amount of principal and payments are known, but the amount due can be ascertained only by a long arithmetical calculation,2 is a mistake of fact, and a payment made by reason thereof may be recovered. Thus, where the parties make a mistake in computing the price to be paid for property, in accordance with a contract of sale,3 or make a mistake in computing the amount due on a mortgage,4 or by mistake compute at eight per cent interest on a note which by its terms bears interest at six per cent,5 or otherwise erroneously compute the interest due ;6 or where a principal and agent make a mistake in computing their mutual accounts ;7 or where by mistake the same item is paid twice;8 or where a payment is made under mistake in computing the weight of the articles sold, on which weight the payment is based,9 money paid under such mistakes may be recovered. A and B, tenants in common in land, were arranging a voluntary partition, and A was to take that half of the land upon which improvements were erected, and pay to B the amount necessary to equalize his share. By a mistake in the computation, A paid to B the entire value of the buildings upon this tract, instead of one-half their value. It was held that A could recover the amount thus paid in by him in excess of the amount necessary to equalize his share with B's.10
13Duluth v. McDonnell, 61 Minn. 288; 63 N. W. 727.
14 Lewellen v. Garrett, 58 Ind. 442; 26 Am. Rep. 74.
1 Gould v. Emerson, 160 Mass. 438; 39 Am. St. Rep. 501; 35 N. E. 1065; Peterson v. Bank, 78 Wis. 113; 47 N. W. 368.
2Vorley v. Moore, 97 Ind. 15; Montgomery County v. Fry, 127 N. C. 258; 37 S. E. 259; Steere v. Oakley, 186 Pa. St. 582.; 40 Atl. 815.
3 Norton v. Bohart, 105 Mo. 615; 16 S. W. 598.
4 Klein v. Bayer, 81 Mich. 233; 45 N. W. 991.
5 Stotsenburg v. Fordice, 142 Ind. 490; 41 N. E. 313, 810.
6 Montgomery County v. Fry, 127 N. C. 258; 37 S. E. 259.
7 Spencer v. Goddard, 62 N. H. 702.
8 Johnson v. Saum, - la. -; fl8 X. W. 599.
9McRae, etc.. Co. v. Stone, 119 Ga. 516; 46 S. E. 668.