The scene
The scene
Mara and Nico both started full-time jobs at 22. Same salary, same city, same career trajectory.
Mara opened an investment account at 25 and put in $400 a month into a low-cost broad-market index fund tracking something like the S&P 500. She has done this every month since. She is now 55.
Nico thought about it at 25, 26, 27, 28. He kept meaning to. He started at 35 and has put in $400 a month into the same kind of fund. He is also 55.
Both invested the same monthly amount. Both used a similar broad-market index approach. Neither withdrew along the way.
Using the historical real return of the S&P 500, which has averaged around 7 percent annualised after inflation since 1928 according to data from Yale and Goldman Sachs research, the difference at 55 between starting at 25 and starting at 35 is striking.
Mara's account, with 30 years of $400 monthly contributions and 7 percent real annual return: roughly $487,000 in today's purchasing power.
Nico's account, with 20 years of the same contributions and the same return: roughly $209,000.
Same monthly amount. Same instrument. Same return assumption. The 10 years Nico kept meaning to start were worth around $278,000 in real terms. More than the next 20 years of contributions would produce, because early years have the longest time to compound.
The past 100 years of S&P 500 data are what these numbers are based on. The next 30 years could produce different returns. Returns vary, markets correct, inflation changes. But the underlying math of compound growth (early years compound more than late years) is a pattern that has held across every long-term market in modern financial history.
What your brain just did
What your brain just did
Our minds discount the cost of waiting because the cost is invisible until decades later, by which point the years are gone. Nico is not lazy. His brain simply could not picture the size of a compound effect spread over 30 years, the way all our brains struggle to imagine numbers that grow non-linearly. This behaviour has a name: Hyperbolic Discounting.
What to do instead, in one move
What to do instead, in one move
The behavioural pattern is the point. The math of compound growth, applied to long historical averages, shows that delay has a cost that grows non-linearly. What anyone does with that information is a personal decision, made in their own circumstances and ideally with appropriate professional input.
TL;DR
- Situation: You understand long-term saving and compound growth in principle. You keep planning to start. You have not started.
- What your mind does: It treats the cost of delay as small because it lives in the distant future, while the friction of starting lives in the present (this is called Hyperbolic Discounting, see below).
- Consequence: Using long-term S&P 500 historical averages (around 7 percent real return), 10 years of delay on a $400 monthly contribution can mean a difference of $200,000 or more in real terms by retirement age. Past performance does not predict future performance.
- What to do: Many people who follow research-based approaches automate contributions early, even at small amounts, so that the decision is made once rather than monthly.
What to do
- Many people find that opening an account today, even before they feel ready, removes the recurring decision.
- A common approach is to start with a monthly amount you do not feel, then increase later.
- Automating contributions on payday is a structure used by people who want the decision out of their hands month to month.
- Increasing contributions when income rises, before lifestyle absorbs the increase, is another approach documented in personal finance research.
What not to do
- Do not assume that waiting until you "know enough" is a neutral choice. The math of compound growth treats waiting as a cost that grows over time.
- Do not skip months because "this month is tight". The brain that says "next month" is often the same brain that said it last month.
- Do not chase complicated strategies before you have a basic plan in place. Research on personal finance behaviour consistently shows that starting beats optimising.
The most expensive year of your investing life is the year you did not invest, based on what history has shown about compound growth.
Want to understand why this happens?
Hyperbolic Discounting is the brain's habit of weighing rewards and costs by how close they are in time, not by how much they actually are.
The cost of waiting to invest lives in the distant future. The friction of starting (paperwork, decisions, choices to make) lives in the present. The brain compares the two and the present often wins, because the present is real and the future is abstract.
The math of compound growth is the math of patience. A dollar invested at 25 has 40 years to potentially grow before retirement. A dollar invested at 35 has 30 years. The difference is not 25 percent less time. Using the historical S&P 500 average of around 7 percent real annualised return, the difference compounds into something much larger because compound curves bend upward, not in a straight line.
It is not you. It is how every human brain handles long-horizon decisions.
What the research found
What the research found
Researchers tested this with simple choices. People asked to pick between $50 today and $100 in a year overwhelmingly picked $50. People asked to pick between $50 in five years and $100 in six years overwhelmingly picked $100. Same gap, same trade-off. Distance from the present changed the answer.
One thing is clear: the past does not predict the future. The S&P 500 has produced a 7 percent real average over the last 100 years, but the next 30 years could look different. What is more reliable than the specific return number is the behavioural pattern. Most people who delay long-term saving find it harder to catch up later, regardless of what returns turn out to be.
"Our minds prefer immediate rewards over delayed ones, even when the delayed reward is bigger. Time discounts cost in a way the math never agreed to." — Dan Ariely (paraphrased from Predictably Irrational, 2008, chapter on present bias and the cost of waiting)
This is called Hyperbolic Discounting. Dan Ariely, Predictably Irrational (2008).
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