add consecutive number for each individual with multiple rows per person

Hi

I have a file that contains multiple rows per individual, each with a different date.

I'd like to allocate a consecutive incrementing number for each individual, like the 'time' column below. This is just a one-off thing I need to apply to this dataset to allow further analysis - doesn't need to be dynamic.

I'm unable to attach a file but below is how the data looks (my file has approx 1k records, 200 ID codes). There is unique identifier for each 'person' but a varying number of rows for each person. It's already sorted by ID and date, so the date variable doesn't need to be used. I would like to find a way for excel to add the 'time' column.
E.g.

ID. date. time
ID1 -- 3/apr/15. 1
ID1 -- 5/june/16. 2
ID1 -- 2/mar-17. 3
ID2 -- 1/jan/13. 1
ID2 -- 5/mar/15. 2

I feel that there should be a simple way to do this but am struggling to formulate the question. I'd be very grateful for any tips on how to achieve this. Thank you for reading!