In Crystal Reports you may have several reports with similar formulas. In you have Crystal Reports Enterprise you can copy formulas to the repository, but many people do not have this option.
To copy formulas from a report, drag the formulas to be copied from the Formula Fields section of the Field Explorer into an empty section of your report. You can always create a new section to put them into because once they have been copied you can delete them from the report.
Open the report(s) you want to copy the formulas to and if necessary, create a blank section within the report. Copy the formulas from the original report and paste into the blank section. The formulas will then appear in the Formula Fields section of the Field Explorer of the report you have pasted into. They can then be deleted from the area of the report itself and used appropriately.