I am also asking about how to simulate annuity plan payout by DIY, instead of relying on insurance companies.
It cannot really be done.
The insurance companies (and governments) offering life annuities are pooling longevity risk, something you cannot do on your own. Lifespan is a variable. Most people cannot predict their death dates with any great precision, but over a large enough population actuaries can calculate life tables and probabilities with excellent precision, then set premiums and payouts based on those aggregates. And back those life annuities further, if necessary, using reinsurance, profits, other assets, and/or general tax revenues, as applicable. You don’t have any of these abilities either.
In the Singapore context, just buy whatever longevity insurance you want to get from the government first (CPF LIFE), in maximally potent longevity insurance form. That’d be a payout start date at age 70, Enhanced Retirement Sum at age 55, Escalating Plan, and your spouse/partner the same. If you want to step outside that particular recipe you can, but that’s the particular recipe that offers the maximum available longevity insurance attributes within that particular program. If you still want more than that amount of longevity insurance, no problem, go find the best deal available among the life annuity providers I’ve listed in the other thread.
To be clear, I do not recommend buying “too much” longevity insurance. That’s not a real world problem with CPF LIFE due to ERS caps, so set that aside. Longevity insurance should be enough to preserve a decent, dignified, real (not nominal) retirement lifestyle for your entire lifetimes (including spouse/partner). But it doesn’t have to be more than that and probably shouldn’t be.
Another interesting question is whether you should rely solely on Singapore dollar denominated longevity insurance. Although the probability is extremely low, I cannot totally rule out a national calamity. Ultra conservative households sometimes decide to nail down a couple life annuity income streams, including one or a couple offshore, for precisely this reason. I have mixed feelings about that since it’s rather expensive, but I can understand the argument.