NYT does a good job relative to most calculators but it is still a calculator and consequently limited.

The big differences then are accuracy and ease of use. On accuracy, there is a difference both in how the numbers are calculated (we use our financial modeling back-end) and the quality of the assumptions used - we have local data sets for transaction expenses, real estate taxes, income taxes etc - NYT uses default values, like 28% for your marginal income tax. This means they end up overstating the tax advantage for lower incomes and understating it for higher incomes). We are also much easier to use, precisely because the user is not relied on for all of the important assumptions - we know your tax rates, we know which mortgages are available to you etc.

Hope this is helpful. Happy to answer any other questions.