We made a simple calculator that does just that: it uses the 4% rule and your savings rate to calculate the number of years before Financial Independence. I'll explain how it works and what it's useful for, but also a few flaws and why it's only a "rule of thumb" calculator. I will also show how anyone can include this calculator to their blog or web page. Finally, a few terms of use and disclaimers. Let's get into it, but first, here's the calculator:

How It Works

The main idea is to see the positive impact of delayed gratification, or how much today's efforts can benefit you in the future. In other words, by not spending all your take-home income now, how much faster (than usual) can you retire?

The calculator makes a few assumptions, some of which can be overridden in the “more options” section.

  1. What is your Savings Rate:

Your savings rate is the % of your net yearly income that you don't spend, but “save” instead. For example, if you make $50k a year after tax but only spend $25k, then your savings rate is 50%.

2. What you do with your savings:

The assumption is that your savings are invested, not kept on your checking account. This means they produce a return. The default assumption is that they are invested in the stock market, in broad-based index funds, and that the average return over the period is 8%. If you have a different ROI, you can change that in the “return on investment” field under “more options”.

3. How much you earn:

This is an interesting parameter because it is optional for the sake of this calculator. No matter what you earn, assuming you are not changing anything else than the savings rate, the calculator’s output will be the same. The reason for this is that our calculator assumes that what you are spending now is what you will be spending when retired, so the proportions remain the same: while you increase your income, the calculator increases your target FI amount proportionally and thus the number of years remain the same. Try it! If you save 25% of your net income, whether you make $24k or $500k a year, you will reach FI after 26 years. If you do change the “starting investment” or the “expenses when retired” options however, then the amount you earn will impact the calculations a lot. See below.

4. How much you already have invested:

You may or may not already have some money invested. By default, the calculator assumes you don’t, which shows a neat “starting from scratch” scenario. If you are ahead, you can change your “starting investment” in the field with that name under “more options”. If you do so, you will have to make sure your “yearly net income” is correct because the results will be out of whack otherwise.

5. How much you will spend when retired:

As mentioned above, the calculator considers by default that you will spend as much when retired as you do now. This is rarely the case, but personal situations may differ. If you know your yearly expenses will be different, then type that amount in the “expenses when retired” field under “more options”. If you do so, this will change your FI target and you will have to make sure your “yearly net income” is correct because here too the results will be out of whack otherwise.

What to do with this info

This calculator is interesting because it gives you a general understanding of how important your savings rate is for your future. You’ll see that if you manage to live consistently under your means, you can get to financial independence and even retire quite a lot earlier than the usual retirement age.

Personal finance is not always as easy as it should be and a simple calculator like this helps with streamlining the information and it highlights the importance of one single factor.

For example, if you only save 10% of your take home pay, you can retire before the age of 60 (assuming you start at 20 years old). If you save 20%, you can reach FI in under 30 years and retire before the age of 50!

Of course, this is not a fool proof, guaranteed formula. Many things could go wrong in the span of a lifetime, and they usually do, to some extent. But it’s a good place to start when you want to get serious about your financial wellness.

The flaws in the “rule of thumb”

As mentioned above, this “rule of thumb” calculator has a few flaws that you may be interested in knowing.

Inflation: the value of a dollar today will most certainly not be the same as a dollar in a few years, let alone 20, 30 or 40 years from now. You could mitigate this flaw a little by entering a “expenses when retired” that is adjusted for inflation. This will result in adjusting your FI target and should get you closer to reality, but you’ll have to calculate the inflation adjustment yourself.

Increase in income: it is likely that your income will increase overtime, even after inflation. It doesn't matter at all for the sake of this calculator if you intend to increase your spending proportionally, thus retaining the same savings rate, but if your savings rate evolves over time (hopefully increases), then the results you will be getting from the calculator will be somewhat incorrect (hopefully pessimistic).

Other income and unusual expenses: this calculator is only based on your usual income and expenses. It does not include buying a house, paying for your kid’s college, or a new car. It does not account for special bonuses you think you’ll get or even social security payments when you retire. These matter a lot in terms of your net worth and your FI target but can’t be included in this calculator.

Different growth rates: the calculator considers only one ROI, but in reality, you may have invested in different asset classes (real estate, equities, crypto, ...) and they may provide different returns. Accounting for those separately would be much more accurate.

Saving your results: the calculator does not save your information. It could be useful to come back to your inputs after a while and see how they compare, or just keep you accountable, but this is outside of the scope of this tool.

There is a solution: if these flaws bother you, create an Oakify (oakify.ai) account! It’s free and Oakify provides a powerful financial projection and a goal setting feature on top of its net worth tracker. Also, your data will be protected by the highest level of privacy thanks to end-to-end encryption (only you can read your data, even Oakify’s staff couldn’t look at your data, even if we wanted to).

Add the calculator to your blog!

You can add the calculator to your blog in 2 lines of code, literally. It is meant to be a shareable tool for the community of people interested in furthering their financial independence and taking control of their money. So go ahead and add it to your blog, but make sure you understand the terms of use for this calculator, both as a user and a publisher (if you include it in your site).

The 2 lines:

<script src="https://oakify.surge.sh/js/oakify-savings2fi.js" defer></script>

Some options:

When you add the calculator, you can specify options to be populated by default. When your readers open your page, the calculator will show all the inputs you specify and the results you want. This may help make your point instead of copying a screenshot. Each attribute is optional, so feel free to include only one, two, all of them or none of them. Here is the necessary code change:

<script src="https://oakify.surge.sh/js/oakify-savings2fi.js" defer></script>

What these options mean :

  • savings: the savings rate
  • starting: the value of “starting investment”
  • roi: the return on investment
  • income: the yearly net income
  • retired: the yearly expenses when retired
  • show-options: pass the value “1” if you want the calculator to expand the options by default, which is recommended if you change some of them.

How to add to a Wordpress page:

On a new line, click the “add block” icon (right), then choose “custom HTML”. From there, simply add the code and you’re done!

How to add to a Ghost page:

Very similar process, on a new line, click the “add card” icon (left), then choose “HTML - insert a raw HTML card”. From there, simply add the code and you’re done!

Include it multiple times in the same page:

If for some reason you wanted to include the calculator multiple times in the same page, you could. In that case, the second line (starting with “<script”) is necessary only once.

Terms of use and disclaimer


This calculator is provided as is, with no guarantee of availability or exactitude whatsoever. It does not constitute and should not be construed as financial or investment advice.

Terms of use:

These terms apply to anyone using this calculator (the tool), which means anyone reading or editing the inputs and outputs of this tool. The tool and the brand (Oakify) are the property of OAKIFY TECHNOLOGIES PTE. LTD. (the company). The company does not grant users or anyone to retro-engineer the formulas used in the tool. Its source code shall not be edited, copied or reproduced without the full written consent from the company.

The company shall not be liable for any use or misuse of the tool or the interpretation of its outputs.

Terms for publishers:

The company is granting the rights to any publisher to publish the tool on their site, as long as the publisher does not publish or promote any harmful material, violence, pornography or discrimination.

The company does not provide any rights to the brand and does not assume or authorise you to assume, promote or insinuate any partnership between you, your site or business, and the company or the brand.

The company reserves the right to update these terms and the company reserves the right to deny any publisher, without justification, the right to publish the tool.