Flex % on expenses for Monte Carlo mode

Allow certain expenses to “flex” lower in Monte Carlo trial years with poor market conditions to improve overall chances of success.

53 votes

Tagged as New feature

Created 11 January 2022 by Kyle Nolan

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  • 11 January 2022 Kyle Nolan created this task

  • 11 January 2022 Kyle Nolan edited this task

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    I think this will be a useful feature, even with a simple implementation. Obviously there are many ways you could implement the flex % logic.

    I just had a random idea for a method - for a each iteration of the monte carlo, after every sim year a “mini monte carlo” would be computed for the remaining years to determine probability of success status for a target goal. Flex spending would be implemented for years when future probability of success fell below a threshold.

    This method would be (n^2 + 3n)/2 more computationally costly (n= # of sim years). It would be less costly if fewer iterations were used for the mini monte carlos.

    07 February 2022
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    This would be neat and I think could be added to expenses as a normal feature (by which I mean, not exclusive to the Monte Carlo analysis).

    Add an option to expenses to decrease by a % amount if there is insufficient funds, similar to the drawdown % on cashflow priorities.

    For instance, I would add my annual vacation expense as able to have a 100% reduction, but my healthcare expense might be 0% and living expenses might be 10%.

    07 February 2022
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    Sounds like what is included with this calculator. Good idea.

    18 April 2022
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    See “Spending Models” tab in for some ideas on how the models can work.

    20 April 2022
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    My two cents. 1. could this be setup as a Discretionary Spending cash-flow priority instead? This way it wouldn’t be limited to Monte Carlo mode. 2. It could also just be a special type of expenses, that can be reduced to 0. You’d just need a way to signify in the projection when it is reduced. Partial and Abandoned Goals seem like a decent fit, but it could also be in it’s own category.

    A global flex % for all expenses doesn’t feel specific enough.

    22 April 2022
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    I love the idea of using it as a cash-flow priority!

    22 April 2022
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    Jackie from discord also brought up the point about needing to specify things like line of credit with a minimum payment option. e.g. a line of credit with a $500/month planned amount, but with minimum payment option of $100/month.

    30 April 2022
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    +1 for this feature, particularly useful for FIRE where you often have discretionary spending early on. There is a good article here about discretionary spending and how it relates to FIRE and the 4% rule:

    29 May 2023
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    Jumping in here at Kyle’s suggestion as I had a similar request.So like in my case, I really like cars, so I’ve modeled owning two and alternately replacing one of them every 4 years. But what if the market is bad or a big random expense pops up, I want to simulate deferring that discretionary purchase until things get better. Maybe even with a limit to how long to defer since buying a fresh new car every 8 years is a want, but eventually replacing transportation can be a need for safety/on-going MX costs.

    Practically speaking I think the answer would be delaying the sale of the (as entered in the UI) and subsequent recurrent purchase, until some condition is met such as last year’s withdrawal rate, or trailing average of last x years; or market based with a floor to trigger delay followed by a required rebound to trigger sale and repurchase. Or maybe there’s a practical way to control a discretionary fund I haven’t figured out that’s filled for a single purpose based on certain conditions that can trigger the car purchase and would only fill based on certain model conditions.

    As you can see I’m not sure the best way to model something like this so hopefully everyone here has ideas to help Kyle out :)

    24 July 2023
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    IMHO, this is probably the single biggest missing component in PL.

    A good example of how this is handled is found in the link below.

    You basically have a spending flex and flex threshold allowing you to auto modulate large ongoing expenditures each year to stay balanced. For example, I plan to go on yearly vacations, but setting an arbitrary yearly expense of $50K keeps that expense static even in downturns. A savvy retiree (which anyone using PL likely is!) would of course adjust these large expenses down to avoid a shortfall.

    I hope to see this soon!

    01 January
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    As a new user, I agree “IMHO, this is probably the single biggest missing component in PL” as a new user.

    If 1929 happens, I am not spending big $$$ on vacations. And would reduce my expenses.

    02 April
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    I’m voting this up, but more for the plan and cash flow prioritization changes than for Monte Carlo simulations.

    15 May