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What is Rule of 115?

A Rule of 115 computes rule of 115 from the inputs you provide. It applies the standard formula to the values you enter and returns the result instantly, without sending any data to a server. Free Rule of 115. The.

Rule of 115

115 / rate% = years to triple money. Quick mental.

Inputs

%
$

Years to Triple

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Breakdown

Rule of 115
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Exact
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After 30 years
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Triplings in 30 years
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About

Rule of 115 (analogous to Rule of 72 for doubling). 115 / rate = years to 3×. 7%: 16.4 years. 9%: 12.8 years. Useful mental shortcut. Exact: ln(3) / ln(1+r) ≈ 1.0986 / r. Combined with Rule of 72: see how money compounds.

Formula

years = 115 / rate%; exact = ln(3) / ln(1+r)

Frequently asked questions

How accurate is the Rule of 115?

It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.

Is the Rule of 115 free to use?

Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.

Are my inputs saved anywhere?

No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.

Can I use the Rule of 115 on my phone?

Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.

Does the Rule of 115 work offline?

Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.

How do I report a bug or suggest improvement to the Rule of 115?

Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.

Can I share results from the Rule of 115?

Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.

Why are the results different from another rule of 115 tool?

Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.

Is the Rule of 115 accurate?

The Rule of 115 applies the standard formula for rule of 115. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.

Is the Rule of 115 free?

Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.

Are my inputs saved?

No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.

How to use the Rule of 115

The Rule of 115 is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:

  • Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
  • Speed: results update as you type. No network round trip.
  • Offline use: once the page is cached, it works without internet.
  • No signup: no account, no email, no rate limits.

Step by step

  1. Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
  2. Read the result as it updates. The number reflects the formula commonly accepted in Rule of 115-related calculations.
  3. Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
  4. Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.

When you would use this

  • Quick estimates: when you need a number now and don't want to open a spreadsheet.
  • Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
  • Comparison: running the same calculation with different inputs to compare options side by side.
  • Learning: building intuition for how the underlying math behaves.
  • Documentation: capturing a snapshot of inputs and outputs at a point in time.

The formula explained

This calculator uses the following formula:

years = 115 / rate%; exact = ln(3) / ln(1+r)

The reason this formula works is rooted in the underlying physics, finance, or biology of the problem. Behind every calculator is a published, peer-reviewed equation or a widely accepted convention. We do not invent formulas; we apply standard ones from textbooks, government tables, professional bodies, and academic literature.

If you are curious about the math, the simplest way to verify is to plug in two known numbers and compare against a known result. The calculator should match published examples to within rounding precision.

About the Rule of 115

The Rule of 115 estimates how many years a lump sum needs to triple at a given compound annual return. Divide 115 by the percentage return: at 8 percent, a portfolio triples in about 14.4 years; at 6 percent, about 19.2 years. It is the natural sibling of the Rule of 72 (doubling time) and the Rule of 144 (quadrupling). All three come from the same logarithmic identity, ln(3) is roughly 1.0986, scaled to fit typical interest-rate behavior.

How the formula works

Years to triple   ≈ 115 / rate(percent)
Exact form        = ln(3) / ln(1 + rate)
Rule of 72        = 72  / rate (doubling)
Rule of 144       = 144 / rate (quadrupling)
Worked example: A 100,000 dollar Roth IRA at 7 percent real triples to 300,000 in 115/7 = 16.4 years. The exact answer ln(3)/ln(1.07) is 16.24 years, an error of one percent.

Tripling time at common return rates

Annual returnRule of 115Exact
3 percent38.337.2
5 percent23.022.5
7 percent16.416.2
8 percent14.414.3
10 percent11.511.5
12 percent9.69.7

Pitfalls

  • Confusing nominal and real return. A 10 percent nominal at 3 percent inflation is 7 percent real. Use real return for purchasing-power tripling.
  • Ignoring fees. A 1 percent expense ratio pushes triple time from 14.4 years (8 percent net) to 16.4 years (7 percent net).
  • Mixing simple and compound. The rule only works for compounding. Simple interest tripling at 8 percent takes 25 years, not 14.4.
  • Treating the estimate as exact. Below 4 percent or above 15 percent the rule overshoots by 2 to 4 percent.

Related calculators

Compound Interest Rule of 72 FIRE Calculator CAGR Calculator

FAQ

Why 115 instead of 120?

ln(3) is 1.0986. At a typical 7 to 8 percent return the correction ln(1+r) is slightly less than r, so 115 fits empirical results between 4 and 12 percent better than 110 or 120.

Is the rule better than running the exact formula?

The rule is faster for mental math; the exact formula is more accurate at extreme rates. Below 4 percent or above 15 percent, use ln(3)/ln(1+r). For everyday planning the rule stays within 2 percent.

How does this interact with inflation?

Use real return. At 7 percent nominal and 3 percent inflation, real return is roughly 4 percent, so tripling purchasing power takes 28 years, not 16.

Does this work for index funds?

Yes. The S&P 500 has averaged 10 percent nominal and 7 percent real total return since 1926, implying tripling times of 11.5 and 16.4 years respectively. Past returns are not guaranteed.

Sources: Bengen (1994) on safe withdrawal rates; Damodaran online dataset on historical equity returns. Last updated 2026-05-28.