I don't know of any 'calculators' available. Over the years, several members have done spreadsheets and reported their results here.
There are so many factors involved it's tough to give a general answer. But my recollection is that on average most users find the bread-even point is around 6 to 10 years. After that you're getting the
DVC accommodations for just the amount of the dues.
Some people try to figure in resale value, which of course changes the formulas. If you purchase today, use the program for 5 years, and then sell, you will get some money back which obviously changed the break even point.
There are instances of some who buy and get incentive points, use the incentive and current year points, then sell the contracts within the year. Even doing this, they save considerably over paying CRO prices for regular hotel rooms.
The biggest factor most find is that they tend to 'upgrade' their accommodations over time. The initial analysis to compare to staying at regular WDW hotel rooms is to compare using DVC Studios. But many will stay in a 1-B/R unit or larger. If one compares a hotel room to a 1-B/R the 'break even' point changes, but on the other hand, the member is staying in a much higher 'upgraded' accommodation during that time.