This calculator will find the right time to fire your thrusters in order to estimate a safe landing.
It is well-known that the best strategy for landing is to fire your thrusters on max at the last possible moment - so this tool will find that right moment.
It doesn't support atmosphere and it doesn't take into account the fact that the ship will get lighter as it burns (no Rocket Equation).
Also, no warranty whatsoever.
Enter some values here and press "Calculate":