smitcat wrote: Wed Jan 08, 2025 10:51 am
dcabler wrote: Wed Jan 08, 2025 10:16 am
It's one thing to use history as a very general guide, which I think is unavoidable. It's another to use historical statistics to apply to the future. This is not physics - at least not the type of physics where the analysis is tractable.
Cheers.
Please add more detail as to how to use historical statistics without applying them to the future.
What do you use to apply for the future?
I spent probably a decade looking at withdrawal methods and how to structure things before landing on what I'm actually doing now that I'm retired. And I can backtest with the best of them! I have no idea how many spreadsheets I have sitting on my hard drive for the seemingly endless simulations and experiments I've run over the years.
For me, it was a combination of thinking about relative risk, how risk manifests itself and whether I can change that, and whether I had "enough" to retire all the while trying my best to minimize relying on past results.
Like many, I started by looking at SWR. I also looked at what I consider to be "hacks" to SWR to try and improve outcomes. And there are many, from Guyton-Klinger decision rules, Kitces ratcheting method, Gummy's sensible withdrawals, Hebeler's autopilot, etc. The problem to me wasn't that using a lower SWR would reduce the odds of failure or that any of these hacks might improve outcomes. Rather the problem to me was the nature of failure itself - that is, running out of money before I planned. And I didn't want to rely on anything that wasn't systematic to avoid running out of money.
I briefly looked at a fixed % of remaining of portfolio since such a method would theoretically last forever. But that required me to figure out a percentage. And I had no way to do that without directly using past statistics and perhaps adding some padding to it.
I then discovered what was originally called "the actuarial method" which is amortization. First with a paper that discussed a method called ARVA by Waring and Siegel, then VPW from longinvest, and finally a 2 part series on the Bogleheads blog from Siamond. My own withdrawal spreadsheet is heavily influenced by Siamond's blog post. Later on, ABW and finally TPAW from Ben Mathew also appeared on bogleheads. What attracted me to amortization methods was that instead of all of the risk piling up in the very last withdrawal like 4%/SWR does, it spreads it out over all withdrawals, resulting in withdrawals that vary. So instead of a risk of being fully depleted, which I would consider to be a disaster, the risk is now that any single withdrawal might be too low to keep the lights on.
Note: amortization withdrawals are based on the same math used for loan calculations. And these calculations require a "rate". For withdrawals, the rate is a real rate of return. VPW, for example, uses fixed numbers based on long term worldwide real returns for stock and bonds. Other methods might use some sort of predicted future returns based on CAPE, or what's published by various research firms and investment houses. When calculating withdrawals, you always use the latest predictions.
Note: this is definitely a number that is one way or another extracted from historical returns. Historically, at least, it doesn't appear that there has been a huge sensitivity to the rate chosen due to the fact that there is at least a little bit of self-correction in the way the math operates. Future? Who knows.
After thinking on this more, I ultimately decided that I wanted to start everything with a base of fixed, real income. What that means is that I'm relying on what is effectively a TIPS ladder. 3 ladders, actually: 2 SS bridges and 1 that lasts until we're in our mid 90's. This covers the vast majority of our nondiscretionary spending. This plus distributions from our stock and a small withdrawal from our stock will cover all of our nondiscretionary spending. It would really require an unprecedented event for the amortization based withdrawal from stocks to ever be so low that, when added to the other sources of fixed income would be such that we'd have to scramble to make up the difference.
The decision to retire always started with running my amortization spreadsheet and looking at the results to see if what popped out was "enough" to pay our nondiscretionary expenses with sufficient upside for lumpy and discretionary expenses.
Then there are contingencies
- We have I-bonds that start to mature in our mid 80's. Here the current plan is that if good health is smiling on at least one of us, we'll consider purchasing SPIAs with this money. Or perhaps it can be used to supplement long term care expenses or even extend the TIPS ladder. The point is we have options.
- We have sufficient discretionary spending capacity such that if the current projected SS shortfall is realized as an actual benefits reduction, we can pull from that to make up the difference. We aren't even coming close to spending the full amount we could today from the discretionary bucket, so we just keep what we don't use invested.
Bottom line is that there's no escaping looking at the past in some way. And for us that means
- The source of the "rate" for amortization, though the withdrawals seem fairly insensitive to this having a pretty wide range - at least for our needs
- The fact that what we do need to withdraw from stocks for nondiscretionary spending is fairly small - small enough that if this withdrawal was too small to complete what we need for spending, we'd probably just take the extra out from discretionary and keep going if that ever happened.
Personal finance is, as they say, personal. This is just an example of how we chose to put things together based on the risks we care most about and how our portfolio progressed during our accumulation years. The future, as they say, is uncertain and my imagination can easily come up with scenarios that can break this - and none of them involve an asteroid. The price to pay to mitigate those scenarios is more than we're willing to pay.
Cheers.
"Repeating a thing doesn't improve it." Quote from Inman, as played by Jude Law, in the movie "Cold Mountain"