The article examines a group of secular accounts, dating between 1434 and 1446, kept during the building of Tattershall Castle in Lincolnshire, England. To explain and illustrate the methods shown in this group, reference will be made to other building accounts with dates ranging from 1237 to 1538. The accounts are compotus rolls, designed to provide annual statements of receipts and expenditure. Each Tattershall account consists of a series of paragraphs. In the first is stated the name of the person rendering the account, three of the accounts being attributed to Thomas Croxby, overseer or supervisor of the works of Ralph, Lord Cromwell, and the fourth to John Southell, clerk of the works. In the rolls for 1438-40 and 1445-46, which appear to be fair copies of a final account, the sum of the items in each paragraph is put at the end of it, in the centre of the page, in an orderly fashion. A closer examination of separate paragraphs leads to the deduction that the compotus rolls have been drawn up by reference to other, more detailed, books and papers and provides some indication of their nature. However, the accounts are too fragmentary to do more than sketch the stages in rendering an account.