Legal Question in Real Estate Law in Maine

This situation is one that is best settled by agreement. It is possible to create a mathmatical formula that takes into account the final net equity of the property and a ratio created by the amounts each party put into the down payment and their contributions to the mortgage payments over the years (which have served to reduce the principal), but you both need to agree on what the elements of the ratio are and apply them evenly. There is the issue of improvements to consider if upgrades have been made. Taxes and insurance are not direct costs of the mortgage, but were necessary to keep the property current to get the property to the present sale. Finally, if only one party has lived there for some period of time, then full credit for the mortgage payments in a formula does not take into account the benefit they received for living there. The party that moved out may have had to pay for rent somewhere else at the same cost as the mortgage so it would not be equitable to give the person that stayed full credit for mortgage payments made while applying zero credit to the person who had to rent during this time.

So there are too many variables for an exact answer in an email context, and your question referred to some of the figures but did not address other variables that may also apply. A lawsuit to get a Judge to decide is costly. Some folks agree to disagree, but if the difference is a few thousand dollars they could agree to split it. Some folks will hire a lawyer/mediator to act as a neutral and meet with the parties to try to reach a binding settlement before the actual sale and closing.