Friend-of-the-blog James sent in a great question this week. Let’s get him an answer.

## The Scenario

James has a Health Savings Account (HSA)** through his work.

He’s able to stow away $7200 per year *tax-free*. And he can invest that money—sweet!

But James’s HSA has a serious flaw: it charges James $25 whenever he makes a “trade.” In this context, a “trade” can be thought of as *any instance where James invests his HSA money*.

So James is faced with an interesting problem…

***Note: if you aren’t familiar with an HSA, read this. My friend Roger highlights all the important stuff you need to know. *

**The Problem**

If James invests money every month, he’ll be charged $25 every month. These fees destroy potential profits!

Instead, James *could* invest every other month, every third month, or even only twice a year. This would reduce the number of $25 fees he pays. That’s good!

However, this infrequent investing schedule means some of James’s money would be “sitting on the sidelines,” not invested in the market. And as any good finance blogger would tell you, **time in the market** is a key to long-term investing success. The sooner James invests his money, the better.

What should James do?

Invest every month and pay more fees?

Or invest less frequently and see less growth?

## The Math

Let’s see what the math says. We’ll build a little model with the following assumptions:

- James adds $600 per month to his HSA—and can invest it if he chooses.
- James will see 7% annual returns on his investment
- Note: I
*love*pointing out how*actual returns*from the stock market*never*look like*average returns*. But when making decisions like this one, using average returns is so much easier.

- Note: I
- There’s a $25 fee whenever James invests.
- We assume zero on-going expense ratio (FZROX and other Fidelity funds have no expense ratio)
- Any money that’s
*not*invested earns 0% return. It just sits in James’s HSA account.

## Option 1: Invest Every Month

First, let’s look at James’s situation if he invested every month—and paid that $25 fee every month!

Before we even start, realize this: $25 out of $600 is **4.2%**. That is a *huge* fee to pay. But it’s only a one-time fee.

Turns out that the long-term effect of these one-time fees is fairly minimal. That’s good news!

Over 30 years, the fees act as the equivalent of a **0.142%** expense ratio. If you know anything about expense ratios, you know that’s *reasonable*.

Instead of returning the true 7.00% per year, James’s investment only returns 6.85%.

It will cost him $29K out of what could have been $706K.

That’s a 4.2% drag (hey! It’s our 4.2% friend again)

Not a bad price to pay for access to investments.

## Option 2: Invest Every Other Month

Let’s repeat the process, except James will now invest every other month.

James saves up $1200, invests it, and pays $25. This is “only” a 2.1% fee on his principal. But he didn’t have any money growing during Month 1.

The trade-off pays off.

The fees equate to only a 0.08% expense ratio. His investment return is 6.91% per year.

He “loses” $17K out of $706K a.k.a. a 2.4% drag on his total portfolio.

Therefore, every other month is *better* than every month.

## Invests Every 3, 4, 5, 6 Months

Let’s repeat the process for every third month, every fourth month, etc. The results are in the table below…

Results | |||||

End Portfolio | Total Drag ($) | Total Drag (%) | Effective Expense Ratio | Annual Return | |

Invest Monthly | $676,237 | $(29,543.22) | 4.186% | 0.142% | 6.848% |

…Every 2 Mos. | $688,990 | $(16,790.23) | 2.379% | 0.080% | 6.914% |

…Every 3 Mos. | $691,918 | $(13,861.72) | 1.964% | 0.066% | 6.929% |

…Every 4 Mos. | $692,394 | $(13,386.51) | 1.897% | 0.064% | 6.932% |

…Every 5 Mos. | $691,890 | $(13,890.38) | 1.968% | 0.066% | 6.929% |

…Every 6 Mos. | $690,898 | $(14,881.91) | 2.109% | 0.071% | 6.924% |

As you can see, James’s most effective plan is to invest his money **every 4 months. **

That’s where he minimized the combination of 1) drag from monthly fees and 2) the opportunity cost from leaving his money out of the market for too long.

Over 30 years, this plan “saves” James about **$16,000** compared to the “invest every month” option. Finding $16K from a 1-hour spreadsheet seems worthwhile.

If you want to play around with the numbers yourself, check out this Google Doc.

## Summary

This problem is another great example of what we learned last week: if math can help solve a problem, pursue that math!

Thank you for reading! If you enjoyed this article, join **7000+ subscribers** who read my 2-minute weekly email, where I send you links to the smartest financial content I find online every week.

-Jesse

*Want to learn more about The Best Interest’s back story?* Read here.

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Great number crunching! Thanks for sharing the spreadsheet so someone can put in their own numbers to check out what is optimal. Saving an extra 16K is really worth taking the time to figure the best answer. However, even paying that $25 fee each month would be better than deciding it not worth paying the fee and not investing.

Thanks Jesse! Coming in clutch per usual. I’ll be sure to comment my questions more within your blog. 🙂

You’re welcome, James! 🙂

I love these posts where you are taking some non-obvious math and laying it out so concisely and clearly! I find it quite inspiring in my own personal finances if I have some sort of “should I do A or B?” to just lay it out in a spreadsheet, do the math, and decide on what the tradeoffs are and what the optimal action I should do is to maximize my returns.

Thanks so much for putting this together!

I’m glad they’re helping you! Thanks for letting us know 🙂

-Jesse