Purchased a property with another person in 1998. We remained equitable partners until April, 2009 when the other party stopped paying their share of the mortgage, condo fees, property tax, upkeep. I continued to pay these fees independently. We have agreed to sell the property ( March, 2015) What is the best way to calculate the per cent equity each person is entitled? the other owner contends it is 50/50. The property is owned as tenants in common with right of survivorship.
The short answer is you're going to need to contact an attorney. Your country/state laws may have unique conditions, interpretations, and precedents. Ideally, you created a partnership agreement when you bought the property that specifies what happens in this situation. If there is no such agreement in place, you're likely going to have to go to court to seek a judgement that your partner's failure justifies a change in the equity ownership. Even if there is such an agreement, it will likely be contested and picked apart for a reason to invalidate it. A competent attorney is also going to be able to determine whether anything else said or done by your or your partner may have contributed to an understanding of 50/50 split regardless of circumstances.
It would seem reasonable to split the equity based on the percentage of overall investment (Total all payments made by each partner, divide by the total combined investments made).
Unfortunately when some partnerships end, reasonability seems to be one of the lesser priorities, as seems to be the case as you describe it.