Project your savings to retirement and past it, then stress-test inflation, a pension that pays less than promised, and the rate you withdraw at. Runs 400 market simulations and reports the share in which your money lasts.
Enough to cover the years before your pension starts, plus roughly 25 times the annual income gap that remains once it does. This calculator works that figure out from your own target income, inflation rate and pension, in your own currency.
A rule of thumb that you can withdraw 4% of your savings in the first year of retirement, rising with inflation, without running out over about 30 years. It assumes a smooth average return, which is why this tool also reports a simulated success rate.
The pot you need grows by roughly the value of the income you lose. The payout setting lets you plan on 100%, 75% or none of your expected government or employer pension and see the target move.