RTCalcExpress is a Delphi component for calculating expressions, entered in Run-Time. It can be installed into Delphi4, 5, 6, 7 and higher. Delivered with sources. The expressions can contain numbers, arithmetic ('+', '-', '*', '/') and logic ('=', '>', '', '>=', '<=', 'AND', 'OR') operators and functions, defined by user (FDU). A priority of the arithmetic calculations is usual - at first multiplication and division, then addition and subtraction. It is possible to change the priority of calculations by the standard way - through parentheses. It is possible to add any quantity of the FDU functions. These functions can be as without arguments and to have the unlimited quantity of the arguments. The arguments suppose any level of an enclosure i.e. these can consist of the expressions, other functions etc. A list of the arguments consists in parentheses. A name of the FDU function is not case sensitivity. A maximal length of the expression corresponds to the length of the Delphi data type AnsiString. The expression can be divided on substrings, which will be calculated one after another. In this case return value will be a result of calculating the last substring. The break-symbol is semicolon. In this case, it is possible to calculate the intermediate meanings, which can be saved in global variables. These variables can be use as the arguments of the FDU functions or as elements of the expressions. The component has 20 global variables.