Leaving the interest part aside for the moment, let's say you've worked from graduation around age 25 until a retirement at 65, or 40 years.
Each year you're paying in, and then when you retire, you're expecting to live until maybe 85, but for game's sake, let's say 95, or 30 years.
You should be able to withdraw 4/3 of your yearly contribution, and the money would last the rest of your life. That's just the principal amount.
But let's say we want to make sure there is enough in the event the person lives an unexpected 40 years into retirement. Then they would draw down at a rate of 2.5% of the original balance, and the fund would last exactly 40 years.
This offsets the fact that the Pension Fund has people still paying in while you're retired.
The way that it is set up in the game: the pensioners never even get 100% of their interest payments, only 60% of that, which is currently 0.01%, so their ROI is 0.006% / 2.5%, or about 1/400th of what they should be getting with 0 interest.
They would have to live 16,000 years to get their money back, without interest.