The $100 Habit: Assumptions and 30 Historical Examples
The numbers behind Lofi Wealth’s $100-a-week investing example.
If you’ve come across Lofi Wealth’s “$100 habit”, this article explains the numbers behind it: investing US$100 a week, following the S&P 500 and giving the investment 30 years to grow.
This article provides the detail behind that idea, so you can check what the figures include, what they leave out and how the same habit performed across different periods in history.
Below are 30 historical scenarios. Every scenario follows the same rules.
The $100 habit: the assumptions
Start with $0.
Invest US$100 on 1 January, then every seven days for 30 years.
Stop before the 30th anniversary.
Do not increase the contribution.
Follow the S&P 500, a widely followed index of large US companies.
Reinvest dividends: any cash distributions from the companies go back into the investment.
Each scenario includes 1,566 deposits: $156,600 contributed in total.
The exact seven-day schedule gives slightly more deposits than assuming 52 weeks per year.
All amounts are US dollars, before tax and fees.
The main results are not adjusted for inflation.
Weekly purchase prices are estimated from monthly historical data; these are not exact trading-day results.
The same habit across 30 historical periods
Every period below starts and ends on 1 January. All 30 periods are complete. These are approximate historical reconstructions, not predictions.
“Contributed” is the money the person put in.
“Growth” is the final balance minus those contributions, including reinvested dividends.
Figures are rounded to the nearest dollar.
Findings, summary:
Average (mean): $1,242,264.
Middle outcome (median): $921,913.
Lowest: $706,083.
Highest: $2,735,326.
Period | Contributed | Growth | Final value |
1967–1997 | $156,600 | $1,601,981 | $1,758,581 |
1968–1998 | $156,600 | $1,932,927 | $2,089,527 |
1969–1999 | $156,600 | $2,399,337 | $2,555,937 |
1970–2000 | $156,600 | $2,578,726 | $2,735,326 |
1971–2001 | $156,600 | $2,200,293 | $2,356,893 |
1972–2002 | $156,600 | $1,718,417 | $1,875,017 |
1973–2003 | $156,600 | $1,227,479 | $1,384,079 |
1974–2004 | $156,600 | $1,477,252 | $1,633,852 |
1975–2005 | $156,600 | $1,375,990 | $1,532,590 |
1976–2006 | $156,600 | $1,335,999 | $1,492,599 |
1977–2007 | $156,600 | $1,355,405 | $1,512,005 |
1978–2008 | $156,600 | $1,154,949 | $1,311,549 |
1979–2009 | $156,600 | $577,050 | $733,650 |
1980–2010 | $156,600 | $692,415 | $849,015 |
1981–2011 | $156,600 | $707,078 | $863,678 |
1982–2012 | $156,600 | $622,864 | $779,464 |
1983–2013 | $156,600 | $615,512 | $772,112 |
1984–2014 | $156,600 | $695,040 | $851,640 |
1985–2015 | $156,600 | $680,062 | $836,662 |
1986–2016 | $156,600 | $549,483 | $706,083 |
1987–2017 | $156,600 | $606,000 | $762,600 |
1988–2018 | $156,600 | $702,983 | $859,583 |
1989–2019 | $156,600 | $569,188 | $725,788 |
1990–2020 | $156,600 | $679,393 | $835,993 |
1991–2021 | $156,600 | $724,499 | $881,099 |
1992–2022 | $156,600 | $810,856 | $967,456 |
1993–2023 | $156,600 | $610,377 | $766,977 |
1994–2024 | $156,600 | $698,246 | $854,846 |
1995–2025 | $156,600 | $806,126 | $962,726 |
1996–2026 | $156,600 | $864,001 | $1,020,601 |
Thirteen of the 30 scenarios finished above $1 million. All finished above the $156,600 contributed, before tax, fees and inflation. The habit produced substantial nominal growth across this set, but the wide range of results matters: a fixed habit did not produce a fixed outcome.
A worked example: 1978–2008
The 1978–2008 scenario is the closest actual result to the $1.24 million average. It finished at approximately $1.312 million. It is one illustration near the average, not the median scenario.
Imagine a person who started on 1 January 1978. They put in $100, then another $100 seven days later, and kept repeating that habit until the end of 2007.
Their own contributions: $156,600.
Investment growth: approximately $1,154,949.
Total portfolio on 1 January 2008: approximately $1,311,549.
The final balance contains both the money they contributed and the growth. It does not mean they put in $1.3 million themselves, and it does not mean the balance rose smoothly. There were market falls along the way.
The mean (average) and the median
The mean is the everyday mathematical average: add all 30 final balances together, then divide by 30. Here, that gives approximately $1.24 million.
The median is the middle of the results when you put them in order, from smallest to largest. With 30 outcomes, it is the average of the two in the middle: $881,099 and $962,726. That gives approximately $922,000. It is a summary of the set, rather than one person’s historical outcome.
Both are useful. The mean shows the average across the whole set, while the median is less influenced by the biggest outcomes. The mean is higher here because a few especially large results pull it upwards. Neither tells us what a future investor should expect.
What is left out?
Tax is left out because it depends on where you live, the type of account or fund you use, and your circumstances. Fees are left out because providers and products charge different amounts. Both can reduce what you keep.
What about inflation?
Over time, the same amount of money usually buys less. That is inflation. The examples above show the dollar balance at the end of each period, without adjusting it for inflation.
But what if you increased your contributions with inflation too? That would keep roughly the same saving effort over time, rather than letting a fixed $100 contribution gradually buy less.
Here is the same historical example used above: 1 January 1978 to 1 January 2008. One person keeps investing $100 a week. The other starts at $100 and increases that weekly amount each January in line with US inflation.
$100-a-week habit | Increasing with inflation | |
Weekly contribution | $100 throughout | $100 initially; about $324 by 2007 |
Total contributed | $156,600 | $343,288 |
Final portfolio value | $1,311,549 | $2,059,521 |
Final value in 1978 purchasing power | $388,345 | $609,816 |
Both final balances in the table are also shown in 1978 purchasing power: what the money could buy in the dollars you started with. Inflation does not remove money from the account; it changes what that money can buy.
The larger portfolio comes from contributing more into the same market, not earning a higher investment return rate. These are approximate historical results in US dollars, with dividends reinvested, before tax and fees.
A $100 contribution in 1967 was also a bigger commitment in purchasing-power terms than $100 in 1996. The main scenarios repeat the same dollar amount, not the same inflation-adjusted saving effort.
Why use the S&P 500?
LoFi Wealth uses the S&P 500 as a transparent, widely documented benchmark. You can look it up, check the assumptions and discuss it with a financial adviser. It allows the habit to be examined without assuming someone knew which individual companies would win.
The index changes its companies over time. Following it does not mean buying today’s companies and keeping that exact list forever. It also covers one part of the market: large US companies. It is not the whole world, a risk-free investment or necessarily the right choice for everyone.
This exercise does not prove the S&P 500 is the best investment. It asks what happened when the habit stayed fixed and the historical market conditions changed.
A bridge between wealth and wellbeing
Lofi Wealth helps people explore wealth-building habits as an alternative to get-rich-quick culture. The purpose of the $100 example is to make the relationship between a repeatable habit, time and investment growth easier to see.
The historical results give the idea context: the same habit produced different outcomes, and the investment choice still matters. Market returns cannot be controlled. The amount someone can sustain and the time they give it are more within their influence. The $100 figure is an example, not a minimum or a recommendation for everyone.
Thirty years can sound like a long time. But thirty years from now, you will probably still have a life: people you care about, things you want to do and decisions you would like money to make easier.
Lofi Wealth’s aim is to build a bridge between wealth and wellbeing. Planning for the future can help people make decisions today, with habits that support the life they want now and later.
Appendix: the basics
What is the S&P 500?
It is an index that tracks around 500 leading publicly traded US companies. Larger companies generally have more influence on its value. You cannot buy an index directly; investors usually use a fund designed to follow it. A real fund has costs and may not match the index exactly.
What are dividends?
Some companies pay part of their profits to shareholders as cash. Those payments are called dividends. Reinvesting them means using the cash to buy more investment units, rather than spending it.
What is compound growth?
It means growth can build on earlier growth. For example, $100 growing by 10% becomes $110. If it grows by 10% again, it becomes $121, because the second increase applies to $110. Actual market returns vary and can be negative. These calculations use the historical return sequence, not a steady 10% assumption.
Does investing every week remove the risk?
No. Regular investing spreads purchases across different market prices, but the portfolio can still fall sharply. A long horizon does not guarantee a profit. These 30 periods overlap heavily, so they are not 30 independent experiments or a reliable measure of the chance of future success.
Appendix: data and calculation notes
Source: Robert Shiller’s ie_data.xls workbook, accessed through shillerdata.com on 1 November 2026. It includes monthly S&P price, dividend, CPI and dividend-reinvested total-return data. Prices are monthly averages of daily closes; dividend observations are based on S&P four-quarter totals interpolated to monthly figures.
The calculation recovers a nominal total-return level by multiplying the workbook’s real total-return price by its CPI. Each monthly observation is assigned to the first of its labelled month. Between observations, a smooth compounded path estimates the index level on each seven-day contribution date.
Each $100 contribution buys fractional units at that modelled level. The final value is the accumulated units multiplied by the level on the 30th anniversary. There is no contribution on the anniversary.
Important approximation: January’s monthly average is used as the 1 January proxy, even though it includes prices later in January. Interpolation smooths daily movements. Weekends and holidays use the modelled calendar-day level, rather than a real trading price. These are monthly-data historical reconstructions, not exact 1 January execution backtests or the official daily total-return index.
The inflation comparison uses the same workbook’s US CPI. In the increasing-contribution scenario, the weekly amount for each calendar year is $100 × that January’s CPI ÷ January 1978 CPI. This is a retrospective model using January CPI, not an assumption that it was known on 1 January. Total contributions are $343,287.89 and the final portfolio is $2,059,520.81. To express either final balance in 1978 purchasing power, multiply it by 62.5 ÷ 211.08 (January 1978 CPI ÷ January 2008 CPI). This gives $388,344.72 for fixed contributions and $609,816.42 for inflation-linked contributions.
Historical performance does not guarantee future results. This article is for education and exploration, not personalised financial advice.
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