We're using Scrum and occasionally find that we can't quite finish a User Story in the sprint in which it was planned. In true Scrum style, we ship the software anyway and consider including the User Story in the next sprint during the next Sprint Planning session. Given that the User Story we are carrying over is partially complete, how do we estimate for it correctly in the next Sprint Planning session? We have considered:

a) Adjusting the number of Story Points down to reflect just the work which remains to complete the User Story. Unfortunately this will mess up reporting the Product Backlog.

b) Close the partially-completed User Story and raise a new one to implement the remainder of that feature, which will have fewer Story Points. This will affect our ability to retrospectively see what we didn't complete in that sprint and seems a bit time consuming.

c) Not bother with either a or b and continue to guess during Sprint Planning saying things like "Well that User Story may be X story points, but I know it's 95% finished so I'm sure we can fit it in."