How much to retire is a simple question but with many answers.

In a very simplified model, the amount is inversely proportional to your age at retirement. The younger you want to retire, the more you will need.

There are various retirement fund "calculators" available in sites such as CPF and NTUC Income. The calculators consider rate of inflation, your age, life expectancy and monthly drawdown amount. The problem with such models is that they are based on drawdown - meaning that you continuously drawdown on your savings till the funds go to zero. Hopefully that's when you kick the bucket.

For me, my retirement model is to have a core savings amount to generate passive income sufficient to fund a simple but comfy lifestyle. In my own model, that would mean a core savings of $3M. I am targeting a monthly passive income of $5 - 6K. In theory, such a model allows me to pass the core savings of the $3M to the next generation, barring unforeseen medical emergencies.