I have been working as a Jr. Developer at my current job for about a year and half. After been at my job for about 5 months I volunteered to do complete rewrite of a very old system that the company had. At the time I said I would do it I was confident it would take a few months at the most, but it has now been over a year since I started to work on the projected and it has proved to be much much harder then I expected.
I just had my review for the 2013 year and it was mentioned that this project is running much longer then I had stated. The biggest things that have caused the project to run long is that I had to learn a whole new coding style (I knew this going in) and I am required to use a framework that was developed in house and is way above my ability to understand and build off of.
Looking at this project now I am fairly confident I can no longer complete it within the extra time given to me (it is now one of my 2014 goal to complete the project). How do I best explain to my boss that I don't think I can complete this project in any decent amount of time and that I should no longer be the developer for this project?
EDIT: Everyone is assuming that I saw this project as a failed project within months of starting it, that is NOT THE CASE. I know the project was going to be hard but I thought I could handle it. Every time I hit a wall in the project and I was able to over come it I thought I could keep going. It has only been over the past few days I have come the realization there are too many walls left and I don't have the skill to do this project.