This question has been asked a bit recently, so I thought I would answer it.
The paid to date is first of call calculated based on the rent balance. E.g. the rent balance may be 50 owing. Assuming the rent is 70 per week (10 per day), this means the tenant is 5 days behind in their rent. So the paid to date is the end date of the current rent period less 5 days. The reason it is the end date is because the rent is due up to the end of the current period.
If the paid to date is incorrect, it probably means the rent balance is incorrect. So the second question tends to be how is the rent balance calculated?
The rent balance is simply the sum of rent due - sum of rent paid. Rent due can be seen by going to the rent periods screen and looking at the rent due column. The rent due can be manually changed from the rent periods screen if required. The rent paid is the sum of all transactions in the cashbook for that tenant with an income group of Rent. This can also be seen on the rent periods screen in the paid column. So if the total rent balance is incorrect, it means the rent due is wrong, or the rent income transactions are wrong. Fixing the transactions or rent periods will also fix the rent balance and also fix the paid to date.