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  • good coastFI calculator

    I've been interested in coastFI ever since my wife got sick, and while she's not here to celebrate it looks like I hit my number already as long as I'm willing to work 1 day/week until 65. Im obviously going to work a little more and save more right now while I can, but comforting to know I really never ever have to take call again. Or stay at a shitty job.
    Here's the calculator I used in case anyone wants to run their numbers https://walletburst.com/tools/coast-...0oBdCirjULcF5M

  • #2
    Nice little calculator. The problem I see is it stops at retirement and simply crunches numbers based on inputs.
    I don't trust the math. If you put in a lower withdrawal rate, the coast fire number increases. It seems the needed amount would increase with a higher withdrawal rate.
    For those two reasons, I would not trust it. It's just a number. Play with the numbers. If the direction is incorrect, it's not worth debugging the model. Maybe I am wrong. But you might be too if you rely on it.

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    • #3
      congrats about hitting coast fire.

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      • #4
        I am not sure if this can be accurate though. For example if I input my age 49, with a target age of retire at 60, and invested amount of 2.1M(my 403B), with a withdrawal rate for 4%, with an annual spending of $120K, the calculator tells me that I have reached coast FIRE. I don't feel that I can just retire and trust the calculator.
        Did anyone do the calculation to see what they are getting?

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        • #5
          Originally posted by FireFox View Post
          I am not sure if this can be accurate though. For example if I input my age 49, with a target age of retire at 60, and invested amount of 2.1M(my 403B), with a withdrawal rate for 4%, with an annual spending of $120K, the calculator tells me that I have reached coast FIRE. I don't feel that I can just retire and trust the calculator.
          Did anyone do the calculation to see what they are getting?
          CoastFI means that you still need to pay for living expenses until retirement but you’ve already saved enough for retirement (given certain assumptions about future growth.)

          Just eyeballing your numbers, an annual $120K spend and a 4% SWR means you need 3MM for retirement. You currently have 2.1MM - it’s totally conceivable that this could grow to 3MM in 11 years. That’s a CAGR of 3.3%.

          Congrats on hitting CoastFI

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          • #6
            Originally posted by Tim View Post
            Nice little calculator. The problem I see is it stops at retirement and simply crunches numbers based on inputs.
            I don't trust the math. If you put in a lower withdrawal rate, the coast fire number increases. It seems the needed amount would increase with a higher withdrawal rate.
            For those two reasons, I would not trust it. It's just a number. Play with the numbers. If the direction is incorrect, it's not worth debugging the model. Maybe I am wrong. But you might be too if you rely on it.
            I think the SWR is what you feel comfortable withdrawing.

            So if you feel safe taking out 4% a year, you’ll need 25X expenses. But if you only feel safe withdrawing 2% a year, you’ll need 50X to retire.

            The calculator is not speaking to the feasibility of your SWR. It’s just reporting how much you’d need to save to achieve the SWR you specify.

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            • #7
              I am also not trusting the math. The numbers that initially entered confirmed that I was at "CoastFI", which is empirically true. Then I made some more extreme assumptions (high inflation, high SWR, lower nest egg number, etc.), and I was still at CoastFI. I am not sure that I believe it.

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              • #8
                Originally posted by SpacemanSpiff12 View Post

                CoastFI means that you still need to pay for living expenses until retirement but you’ve already saved enough for retirement (given certain assumptions about future growth.)

                Just eyeballing your numbers, an annual $120K spend and a 4% SWR means you need 3MM for retirement. You currently have 2.1MM - it’s totally conceivable that this could grow to 3MM in 11 years. That’s a CAGR of 3.3%.

                Congrats on hitting CoastFI
                This is the main difference between this and FIRE. Working one day a week as an anesthesiologist I'll make enough to cover my expenses, so I dont need to add to my retirement accounts. I of course will work a lil more right now (im only working 4 days a week) but plan on cutting back even more in a few years. FWIW I'm putting over 6 figures into my retirement savings this year even though I dont need. Full FIRE I need to work 8 more years at this pace, or take call for 3 years, not going to happen. And I was conservative in my expected growth. I also forgot to include my (small) nyc pension and the (larger) TDA assets, with their guaranteed growth of over 7% (that needs a law being passed to reverse it) that are currently growing at 8% fixed, so I'm sure I'm fine.
                Last edited by billy; 04-02-2022, 12:48 PM.

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                • #9
                  You can also use firecalc for this…under the not retired yet tab just enter the number of years you are going to “coast” to retirement and list amount saved during those years as 0. I like that one because you can also enter future projected income from pension and/or rental properties, etc, as well as varied spending models, projected increases/decreases, how much you want to leave when you die, etc.

                  The math on this one checks out just fine. It’s the assumptions that I guess people aren’t comfortable with (inflation, returns, spending, etc.)
                  Last edited by Anne; 04-02-2022, 01:59 PM.

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                  • #10
                    Originally posted by VagabondMD View Post
                    I am also not trusting the math. The numbers that initially entered confirmed that I was at "CoastFI", which is empirically true. Then I made some more extreme assumptions (high inflation, high SWR, lower nest egg number, etc.), and I was still at CoastFI. I am not sure that I believe it.
                    Given your financial savvy and some of the details you’ve shared about your career, I wouldn’t be surprised if you were all types of FI.

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                    • #11
                      One hiccup in these calculations is that expenses in retirement are not constant. For example we're now late 40s with kids in junior high and high school. They have tons of sports travel expenses, and of course college coming up. They'll soon be driving, cha-ching on auto insurance and umbrella prices, not to mention 1-2 more vehicles for them. And we still have a mortgage of $50k per year for 13 more years. Most expensive ten years of our lives, right now. But in 7 years our daughter graduates college (we hope). In ten years our son. In 12 years the mortgage is paid off. Our expenses could go from X to 1.25X to 0.75X over the next 12 years or be even more volatile than that.

                      You almost need to run a series of Monte Carlo sims with variable outcomes for (in my case) the first 4-7 years, the next 3-5 years, then the next 3-5 years, then the low cost years starting about 12-14 years from now. Depending on how conservative you want to be you can use the 10-20%ile results from each sim as the starting value for the next and get as close to "guaranteed" as there is in this life.

                      On a related note it's important not to run a single MC simulation with very long time periods like 40+ years. There aren't many independent 40+ year time periods in stock market history, so you're getting a truly small n. All that kind of simulation is telling you is that in the last 125 stocks have done well, it hide the volatility of 10-20 year periods and especially considering starting valuations of both stocks and bonds it's probably overly optimistic on a real basis.

                      Also keep in mind how utterly corrosive 8% inflation is, at these rates the purchasing power of the dollar is halved every 5 years. A million or ten isn't what it was even 3 years ago because of the global destruction of fiat currency, all you have to do is look at housing prices to see how much less you can buy with your money.

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                      • #12
                        Originally posted by FIREshrink View Post


                        Also keep in mind how utterly corrosive 8% inflation is, at these rates the purchasing power of the dollar is halved every 5 years. A million or ten isn't what it was even 3 years ago because of the global destruction of fiat currency, all you have to do is look at housing prices to see how much less you can buy with your money.
                        Can someone comment on my line of thought on this. True, if you're holding cash, the inflation will have an impact overtime. But say a typical CoastFIRE person has a house and is paying for the house, has their nest egg in the market in some form of diversified allocation.. shouldn't the tide of inflation also increase their home value and their portfolio in some equivalent way. If an iPhone cost $10,000 in 10 years, shouldn't shares of Apple be going up as well because they'd be taking in a lot of revenue from a $10,000 iPhone?. Am I too simplistic in this line of thinking?

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                        • #13
                          Inflation definitely favors the haves. Those who have real assets like real estate, or equities will be protected to some extent but you can still lose money in cash like assets or decreasing real wage income.

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                          • #14
                            Well of course I wish she were here to toast this milestone but I'm glad you're sharing with us! I think we are there as well, if I was willing to work to 65. Unfortunately, I feel like something broke in me when I turned 40 a few months ago. I can't see working past 45 some days, others I think I can get to 53 when my youngest finishes highschool. So I guess we'll see.

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                            • #15
                              It’s funny that people are only just now realizing that they’re so far beyond prepared for retirement that they think the calculator is wrong… lol

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