42 scenario calculators. Not "here is a formula" - here is your actual situation, played out, so you can see the outcome before you commit to it. Change an input, watch the answer move. For straightforward unit conversion, see Conversions.
What "scenario" actually means here
A plain formula takes one input and gives one output. A scenario calculator models the actual situation - which usually means several things changing together, not one number going in and one coming out. A loan with an offset account is not one equation; it is a running balance that changes every month, against a payment that stays fixed. A grade you need on a final depends on everything that came before it, weighted correctly. That is the difference between a calculator that gives you a number, and one that gives you the number that is actually right for your situation.
Every tool below is built the same way: the real mechanics first, the formula second, and the assumptions stated plainly rather than buried. Where a number depends on something you have to estimate - an interest rate, an inflation rate, a discount rate - that input is yours to change, and the tool shows you how the answer moves when you do.