EllenP,
Unless this property is hugely valuable, you and your ex are crazy to go to court over it. Try to reach an amicable settlement.
Did you both have similar earnings - all lodged to this joint account - while together? If so, then a reasonable outcome would be for you to get your savings back 'off the top' and for the balance to be split 50\50.
If on the other hand, one or other of you had significantly greater earnings during the relationship, then there may be some argument in favour of giving due credit for this. In other words, if two thirds of the money going into the joint account was yours, it might be reasonable to attribute two thirds of the mortgage repayments as having been made by you. Conversely, if your partner's earning were higher than yours, this might be regarded as compensating to some degree for the up-front money provided by you. It's a messy area, and the 'rough indication' you are looking for depends on many factors, some of which I have adverted to above.