A mortgage is the largest arithmetic problem most people ever take on, and small differences compound into very large ones. These work the real month-by-month numbers rather than a simplified estimate.
The three tools here answer different questions. The loan and mortgage calculator is for working out what a loan actually costs, including offset accounts and extra repayments. The refinance calculator is for deciding whether switching is worth it, and it checks the total-interest question that catches people out when a refinance resets the term. The amortization calculator shows the year-by-year split between interest and principal.
The thing worth understanding before any of them: in the early years of a mortgage, almost every dollar you pay goes to interest rather than to the debt itself. That is why an extra repayment early is worth so much more than the same repayment later, and why a refinance that resets you to year one can cost more overall even at a lower rate.