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Add some margin of safety to your FIRE plan

Baptiste Wicht | Updated: |

(Disclosure: Some of the links below may be affiliate links)

If you plan to retire early based on a withdrawal rate strategy, you base your FIRE plan on historical data. So, what would happen if the future is very different from the past?

We obviously cannot predict the future. So, what can we do? We can improve our FIRE plan with some margin of safety!

In this article, we see several ways of adding some margin of safety into your FIRE planning.

The need for some margin of safety

If you plan your FIRE plan precisely for the parameters you know, you risk running out of money during retirement. Here are three examples of things that could go wrong with your FIRE planning.

First, if you need your money to last 50 years of retirement, you could plan everything exactly for 50 years. However, what then would happen if you lived longer than you planned? Theoretically, you could run out of money the day after your 50 years are finished.

Second, With Fire planning, you base your chances of success on historical data. Historically, the stock market has returned about 8% after inflation. If the stock market were to return only 6% on average after inflation, your effective chances of success would be significantly lower than what you planned for.

Third, when you do your FIRE plan, you base your planning on your planned expenses during retirement. But things can change in the future. For instance, you could suddenly have unexpected inflation in some parts of your expenses. If your costs increase by 10%, your entire FIRE plan is at risk.

If you want to improve your chances of succeeding in these scenarios, you must add some margin of safety into your FIRE plan. Fortunately, there are many ways to achieve this.

However, there is a cost to adding some margin of safety to your plan. A safer plan means that it will be more challenging to reach your FIRE goal. You may work longer to accumulate enough money to become financially independent. So, it remains essential to keep a balance between not enough safety and too much safety.

Keep in mind that all these techniques are optional, and you would have to decide for yourself whether you want to include them in your FIRE plan.

Plan for higher expenses

The first way to add a margin of safety to your FIRE plan is to plan for higher expenses.

When computing your FIRE number, you use your yearly expenses as the base. So, your entire FIRE plan is only valid for these yearly expenses. Your FIRE plan only takes inflation into account by default. So, if you increase your expenses by 10% because of a change of lifestyle, you are endangering your entire plan.

So, you have to be careful about estimating your expenses in retirement. It is more difficult than you think to know how much you will spend. And it is impossible to know it exactly. It is still an estimation.

So, a simple way to have a safer plan is to plan for higher expenses than your estimation. For instance, you could plan for 10% higher expenses. So, if you spend 10% more in retirement than planned, your FIRE plan would still work.

But increasing your planned expenses means increasing your FI number accordingly. Adding 10% to your planned expenses is the same as adding 10% to your FI number. So, it will likely take you 10% longer to reach your goal.

It is up to each FIRE planner to decide how much percent they want to add to their planned expenses. Some people are comfortable with having no margin of safety there. Since we can only estimate our retirement expenses, it makes sense to increase this estimation to be safer. I will likely use 10% in my FIRE planning to be safer.

Don’t aim for a 100% FI ratio

In theory, as soon as your FI net worth reaches 100% of your FI number, you are financially independent, and you could retire.

But there is an issue with this approach: Sequences of returns risk. Indeed, not each FIRE starting point is equal. If you are 100% FI at the bottom of a bear market, you are in great shape. But if you are 100% FI at the top of a bull market, you will likely be in trouble once the bull market falls. Of course, we only know these two points in hindsight. But it shows that being 100% FI is not always enough and is market-dependent.

I see two ways of adding some margin of safety to this part of the plan:

  1. You could wait several years after being 100% FI before executing this plan. Doing so would give you an important buffer for the following years.
  2. You could wait until you have more than 100% FI, for instance, 110% FI. A higher FI goal would greatly enhance the chances of success and reduce your susceptibility to sequences of returns risk.

I think that aiming for a higher percentage is what makes the most sense here. If you aim for 110% (or more or less, it is up to you!), you will significantly increase the safety of your FIRE plan.

Once again, you will also increase your time to reach your goal. For example, increasing your goal to 110% FI is the same as reaching 110% of your FI number. So, it will take you 10% longer to achieve that goal.

Aim for a larger success rate

When you choose your safe withdrawal rate, you are likely using the success rate as an essential metric to drive your choice.

The target success rate you choose will impact the Safe Withdrawal Rate you choose and on your FIRE plan. For instance, planning for a 75% chance of success will likely yield a higher withdrawal rate than planning for a 95% chance of success.

So, if you increase your target success rate, you will also have a safer plan. For instance, if you were planning for a 90% success rate, you could target 95% instead.

It is difficult to quantify how much this will impact your journey to FIRE. Indeed, this will only change if you change your withdrawal rate. Maybe increasing your target chance of success does not even change your withdrawal rate. But if it reduces your withdrawal rate by 0.1%, it will significantly increase your FI number and the time you need to reach it. But a lower withdrawal rate will also have a significant effect on the safety of your FIRE plan.

You can test this out with my FIRE calculator. For instance, with an 80/20 portfolio and 50 years of retirement, you need the following withdrawal rate:

  • 4% to get an 85% chance of success
  • 3.8% to get a 90% chance of success
  • 3.65% to get a 95% chance of success
  • 3.2% to get a 100% chance of success

So, you will find your withdrawal rate based on your target success rate. And as you can see, this can make a significant difference in your withdrawal rate. But this could make a very large difference as well in the chance of success of your FIRE plan.

Choose a lower withdrawal rate

Finally, a powerful way to add some margin of safety to your expenses is to choose a lower withdrawal rate.

A lower withdrawal rate means you will withdraw (and spend) less money every year. As such, your chances of success will significantly increase. For instance, if you planned for a 3.75% withdrawal, you could plan for 3.6% instead. A lower withdrawal rate would strongly impact your chances of success.

However, It also means you must allocate more money for your retirement. Therefore, a lower withdrawal rate means a higher FI number and a longer time to accumulate this money.

For instance, with yearly expenses of 100’000 CHF, you will get the following FI numbers:

  • 2’500’000 CHF with a 4% withdrawal rate
  • 2’666’666 CHF with a 3.75% withdrawal rate
  • 2’857’142 CHF with a 3.5% withdrawal rate

So, we can see that the impact of a lower withdrawal rate on your FI number is very significant. So, using a 2% withdrawal just because you want to ensure you can retire does not make sense if 3.25% would already guarantee success.


There are several ways you can use to add some margin of safety to your FIRE plan. They can help significantly in increasing the safety of the plan.

However, more margin of safety does not come free either. Increasing your FI number by 10% means you need 10% more money. So, it will likely take you 10% longer to reach that goal.

So, you need to find a balance of good safety. If you have too much, you will have a lot of money at the end of your retirement period. This may be good if you intend to leave money to your heirs. But it also means that you could have retired earlier.

I will apply a total 10% margin of safety on my FIRE plan. But of course, I will not be financially independent for at least 15 years. So I will have time to review my FIRE plan for many years. Things may change in the meantime.

I believe that adding some margin of safety to your FIRE plan is important. But adding too much will hinder your chances of reaching your FIRE goal. Make sure to not go overboard!

There are other ways you can help your chances of success. For instance, you could be prepared to get some extra income one way or another should the stock market dip too much. Or you should be able to reduce your expenses somehow in a bear market. But these are more reactive measures rather than margin of safety planning.

What about you? How do you add some margin of safety to your FIRE plan?

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Baptiste Wicht started in 2017. He realized that he was falling into the trap of lifestyle inflation. He decided to cut his expenses and increase his income. This blog is relating his story and findings. In 2019, he is saving more than 50% of his income. He made it a goal to reach Financial Independence. You can send Mr. The Poor Swiss a message here.

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4 thoughts on “Add some margin of safety to your FIRE plan”

  1. Another great post! I always enjoy them.
    I‘m quite conservative when it comes to my FIRE planning. I aimed for a historically safe WR of 3.2%. But on top of that I just kept working after I had reached that goal. Which increased my FI number further or decreased my SWR even more depending on how you look at it.
    I think fire folks often see the world as black and white, as FIRE or Non-FIRE. I was like that too, but as soon as I had reached my FI goals working became a lot easier. It makes a huge difference when you‘re not depending on a steady income anymore.
    Working a couple of years past your FI goals significantly increases your safety margins. Everybodys situation is different but for me that was the easiest way to add more safety.

    1. Hi Mark,

      That’s an excellent point! Working a few years after you are 100% FI can make a great difference. Personally, I am more interested in the FI than in the RE but that may change in the future.
      I am sure that being FI makes a nice difference already!

      Congratulations on being FI!

  2. Hi Mr TPS,

    Thank you for this post, I think it is very helpful for everybody that is thinking to reach FI and count on the calculated number based on the expenses according to all the rules we can read in many FIRE blogs.

    About a week ago I come to the realization that for my FI I would have to add 28% on top of the FI value because in my country I’m charged for the capital gains when I sell and the number can even grow.

    This on top of the expenses inflaction that can happen will mean a very larger FI value but I have to try to reach FI and hope for the best. Possible I can’t make to FI but I will die trying. :)

    Luis Sismeiro

    1. Hi luis,

      It’s a great point about capital gains. you need to take them into account in your future retirement expenses. Keep in mind though that your marginal tax rate will be lower in retirement (at least in most countries). So, you may not have to add 28% if that’s based to your marginal tax rate.

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