Need calendar able to create a template for date calculation

Please, recommend an affordable calendar with function to create a template for calculation of project stages dates. There is a process which consists of events A, B, C and D. Date A comes irregularly and unpredictably. Date B is, say, 7 days after date A. Date C is, for example, 10 days from the date B. And D is a deadline calculated from date A. I need, by entering A, to get the rest of the dates shown in a calendar (as opposed to excel spreadsheet) and to be able to change the dates: if B, say, happens ahead of schedule I need to be able to move it and C should change automatically. The whole process is repeated many times but the intervals between the stages are always initially the same, that is why I need a template. Usually there are several processes going on simultaneously, at the same or different stages. Does anyone know a calendar which would show me all the necessary dates and deadlines? Preferably for Windows 7, but Android app or a web-based service will do too. Thank you.