Week 30 Day 6: The Only Timing That Matters: When You Start

A 25-year-old who invests $300/month for 40 years at 10% ends with approximately $1.9 million. A 35-year-old who invests $600/month for 30 years at 10% ends with approximately $1.3 million. The 25-year-old invested half as much money per month but ends with 46% more wealth. The 10-year head start was worth more than doubling the monthly investment.

Starting dates and outcomes (assuming $500/month invested in total U.S. stock market): Started in 2000 (right before dot-com crash): by 2024, portfolio approximately $485,000 on $144,000 invested. Started in 2005: by 2024, portfolio approximately $370,000 on $114,000 invested. Started in 2010 (after the recovery began): by 2024, portfolio approximately $250,000 on $84,000 invested. Started in 2015: by 2024, portfolio approximately $107,000 on $54,000 invested. Started in 2020: by 2024, portfolio approximately $35,000 on $24,000 invested. The pattern: every year you delay costs you real money. Not because you miss specific market moves, but because you forfeit years of compounding. The person who started in 2000 -- right before two devastating crashes -- still has the most money because they had the most time. What if you are 45 and have not started? The same principle applies: 20 years of compounding from now is still vastly better than 10 years from now. Start immediately. The amount matters less than the act of starting. Even $100/month in VTI today begins the compounding clock.

The dominance of starting date (duration) over entry timing is a mathematical consequence of the exponential compounding function. For an investor making regular contributions C with return r over horizon T, the terminal wealth W = C * [((1+r)^T - 1) / r]. The sensitivity of W to T (dW/dT = C * (1+r)^T * ln(1+r) / r) is exponentially increasing in T, while the sensitivity to the entry point (a one-time shift in r for the first period) is linear and diminishing relative to total wealth as T increases. Simulations by Vanguard (2023) confirm that for a 30-year investor contributing regularly, the total contribution timing (when you start) explains approximately 80% of the variance in terminal wealth, while the specific entry date within the first year explains approximately 5% of the variance. The remaining 15% is explained by the path of returns (sequence of returns risk, which is most relevant for decumulators, not accumulators). The policy implication is clear: the single highest-return financial action available to most people is starting a regular investment program immediately, regardless of current market conditions, asset allocation details, or economic outlook. Every month of delay reduces terminal wealth by approximately W * r / 12 (one month's worth of expected compounding), which for a portfolio eventually reaching $1 million at 10% returns equals approximately $8,333 per month of delay -- a staggering opportunity cost that dwarfs any conceivable market timing benefit.