How should I start investing at 18?
The Problem
Everything about this situation is an investing cheat code: no rent, no tuition, steady Guard pay, and a 41-year runway to age 59 1/2. The only thing pointed in the wrong direction is the menu he's choosing from. His bank's shelf tops out at 4.3%, so let's put the actual best option next to it and let the numbers argue.
The Solution
I modeled this in HoneyPlan with the numbers from the question, plus one assumption where he didn't give a figure:
- Income: $1,250/month of Guard pay and college-money leftovers.
- Expenses: $600/month for gas, phone, and spending money, generous for someone living at home.
- Cash: a $4,000 starting balance (my assumption) parked at his bank's 2% savings rate.
- The Roth IRA: $0 today, $625/month, which maxes the $7,500 annual limit, invested in a total-market index fund at 7% expected return.
- The alternative: a CD ladder at his bank's best 4.30%, same $625/month, so the only difference between the two paths is the rate.
One pill on the banner: Play It Safe (CDs). It swaps the Roth IRA for the CD ladder, identical contributions, identical timeline. Toggle it and watch what "safe" costs over 41 years. (His Roth TSP keeps running separately; a Roth IRA has its own limit and stacks on top.)
The Projection
Forty-two years, from age 18 to past the 59 1/2 line, maxing the Roth IRA:
The Results
| CD ladder (4.3%) | Roth IRA (7%) | |
|---|---|---|
| Value at the end of 2067 (he turns 59 1/2 that July) | $864,301 | $1,844,095 |
| Total contributed | ~$311,000 | ~$311,000 |
| Growth earned | ~$553,000 | ~$1,533,000 |
| Tax on the way out | interest taxed as income every year | $0, qualified Roth withdrawals |
| Same plan, but starting at 28 | ~$863,000 | |
First insight: the Roth path passes $1.8 million, and only $311,000 of it is his money. Maxing the Roth IRA at $625/month crosses the 59 1/2 line in July 2067 at $1.79 million (the grid marks it with the Sweet Spot 🍯) and ends that year at $1,844,095, with over $1.5 million of that being growth. And the projection actually understates the gap: CD interest gets taxed as income every single year along the way, while qualified Roth withdrawals are tax-free forever. The 22-year-old version of this question usually starts "I wish I'd started at 18." He's at 18.
Second insight: "playing it safe" costs $980,000. Toggle the pill. Same $625/month, same 41 years, at his bank's best 4.30% CD rate: $864,301 at the end of 2067. The difference between 4.3% and 7% sounds like pocket change; compounded over four decades it's nearly a million dollars. CDs aren't wrong for money with a date on it, but they're a parking lot, not an engine. His long-term dollars can afford the engine.
Third insight: his edge isn't the rate, it's the decade. Run the identical plan starting at age 28 instead and it ends at about $863,000, almost exactly the CD outcome. Waiting ten years and "playing it safe" are the same $980,000 mistake wearing different clothes. Put another way: the first decade of contributions, just $75,000 out of pocket, is worth nearly a million dollars at the finish line. And the 5-year framing in his question is the one idea to unlearn: after 5 years the Roth holds about $45,000, only $7,500 of it growth. Compounding is back-loaded; the boring first act is the price of the third act. Meanwhile the projection shows his money quietly passing a milestone in February 2036, at age 27: the Roth's monthly growth starts exceeding his entire $600/month lifestyle. His money outearns his spending before he turns 28.
Two footnotes on the rest of his plan. The Roth money isn't locked away like he might fear: contributions (not the growth) can be withdrawn anytime, penalty-free, which makes a maxed Roth a perfectly good deep-backup layer behind his savings. And the credit card for gas is a fine credit-building move with one non-negotiable rule: paid in full every month. Our debt-vs-emergency-fund case study shows what 22% APR does to the other side of this math.
The Conclusion
Max the Roth IRA, every year, starting this year. $625/month into a total-market index fund inside the Roth, on top of the Roth TSP he already has. Keep a cushion in savings, but shop around: plenty of banks pay 4%+ on savings accounts, and his bank's 2% isn't a law of nature. Skip the CD ladder for money he won't touch for decades. Get the gas card, autopay it in full, never carry a balance.
He asked how to "make more money" as if the answer were a better product on his bank's shelf. It isn't. The answer is that an 18-year-old with zero overhead and $625/month is already holding the single most valuable asset in all of personal finance: 41 years of runway. The projection just makes it visible: $1.8 million, tax-free, and his money outearning his lifestyle by 27.
Open this exact plan in the full demo, put in your own numbers, and toggle the scenario yourself. Runs in your browser, no account, no email.
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