On updating one record automatically update all records carrying formula fields

On updating one record automatically update all records carrying formula fields

I am trying to build a project management application where each task is dependent on its previous task and each task's End Date becomes the Start Date of next dependent task. End Date of each task is calculated by adding a duration into that task's Start Date. What I want to do is when I edit and update a task's Start Date or Duration, it should update all dependent tasks automatically. So far, I have been able to update only one record (either the next dependent task or any one task or record selected based on a criteria). I can achieve this if, on edit --> On Success, I write a script to update next dependent task and then Update remaining tasks one by one in the view mode which is not practical since there could be 100s of tasks. 

Any help is appreciated.