Addressing Tax Impact with Our Improved Cost Basis Accounting Method

Selecting tax lots efficiently can address and reduce the tax impact of your investments. 

Chart going up and down next to a bullseye arrow

Selecting tax lots efficiently can address and reduce the tax impact of your investments. 

We use advanced tax accounting methods to help make your transactions more tax-efficient. When choosing which lots of a security to sell, our sophisticated method factors in both cost basis as well as duration held.

When you make a withdrawal for a certain dollar amount from an investment account, your broker converts that amount into shares, and sells that number of shares. Assuming you are not liquidating your entire portfolio, there's a choice to be made as to which of the available shares were sold. Every broker has a default method for choosing those shares, and that method can have massive implications for how the sale is taxed. Betterment's default method seeks to reduce your tax impact when you need to sell shares.

In the chart below, you can see the tax impact of an actual $150,000 withdrawal made by a Betterment customer with New Jersey listed as their state of residence. The withdrawal sold some of several ETF positions in a $1,000,000+ portfolio. Assuming tax rates consistent with their input income, Betterment saved this customer $11,122 in state and federal taxes, just by having a better default selling method.

Betterment saves a customer $11,122

  Typical FIFO selling Betterment's TaxMin selling
Ticker Gain/Loss Short or Long Term Gain/Loss Short or Long Term
VTI $23,639 Long $11,771 Long


$10,378 Long $4,410 Long
VWO $7,472 Long $2,628 Long
MUB $7 Long -$3 Short
EMB -$10 Long -$20 Short
VTV $6,193 Long $2,130 Long
VOE $5,571 Long $2,714 Long
VBR $6,704 Long $4,144 Long
ST Gain/Loss $0   -$22  
LT Gain/Loss $59,955   $27,797  

Tax Owed:



*Actual customer withdrawal of $150k in April 2021 as a resident of New Jersey, with input annual income of $220,000 and single tax-filing status with no dependents. This calculation assumes that this customer takes the standard deduction when filing taxes, a state capital gains rate of 10.75%, and federal tax rates on short and long term gains of 40.8% and 23.8%, respectively, both inclusive of the net investment income tax of 3.8%. State of residence and other client information may materially affect the outcome or projection of tax minimization technology. The real life scenario listed in this example may not apply to all clients and is not a guarantee of similar results. Tax savings are net of Betterment’s fee of 25 BPS.

Basis reporting 101

What's going on here? How can internal accounting result in such a drastic difference? First, some background. The way investment cost basis is reported to the IRS was changed as a result of legislation that followed the financial crisis in 2008. In the simplest terms, your cost basis is what you paid for a security. It’s a key attribute of a so-called “tax lot”—a new one of which is created every time you buy into a security.

For example, if you buy $450 of Vanguard Total Stock Market ETF (VTI), and it’s trading at $100, your purchase is recorded as a tax lot of 4.5 shares, with a cost basis of $450 (along with date of purchase.) The cost basis is then used to determine how much gain you’ve realized when you sell (and the date is used to determine whether that gain is short or long term).

However, there is more than one way to report cost basis, and it’s worthwhile for the individual investor to know what method your broker is using—as it will impact your taxes. Brokers report your cost basis on Form 1099-B, which Betterment makes available electronically to customers each tax season.

Better tax outcomes through advanced accounting

When you buy the same security at different prices over a period of time, and then choose to sell some (but not all) of your position, your tax result will depend on which of the shares in your possession you are deemed to be selling. The default method stipulated by the IRS and typically used by brokers is FIFO (“first in, first out”). With this method, the oldest shares are always sold first. This method is the easiest for brokers to manage, since it allows them to go through your transactions at the end of the year and only then make determinations on which shares you sold (which they must then report to the IRS.)

FIFO may get somewhat better results than picking lots at random because it avoids triggering short-term gains if you hold a sufficient number of older shares. As long as shares held for more than 12 months are available, those will be sold first. Since short-term tax rates are typically higher than long-term rates, this method can avoid the worst tax outcomes.

However, FIFO's weakness is that it completely ignores whether selling a particular lot will generate a gain or loss. In fact, it's likely to inadvertently favor gains over losses; the longer you've held a share, the more likely it's up overall from when you bought it, whereas a recent purchase might be down from a temporary market dip. Clearly, the ability to identify specific lots to sell regardless of when they were purchased could get you a better result, and the rules allow an investor to do so.

Yet having to identify specific shares every time you sell is tedious at best, and incomprehensible at worst. Fortunately, the IRS allows brokers to offer investors a different default method in place of FIFO, which selects specific shares by applying a set of rules to whatever lots are available whenever they sell. The problem is that many investors are not even aware there's something they should be overriding, much less which alternative to choose. Upgrading the default method can be a multi-step process through a clunky and confusing interface.

While Betterment was initially built to use FIFO as the default method, specific share identification can have such a positive impact on your tax bill that we’ve doubled down to improve our methods. We upgraded our algorithms to support a more sophisticated method of basis reporting, which aims to result in better tax treatment for securities sales in the majority of circumstances. Most importantly, we’ve structured it to replace FIFO as the new default—Betterment customers don’t need to do a thing to benefit from it.

Betterment’s TaxMin method

When a sale is initiated in a taxable account for part of a particular position, a choice needs to be made about which specific tax lots of that holding will be sold. Our algorithms select which specific tax lots to sell, following a set of rules which we call TaxMin. This method is more granular in its approach, and will improve the tax impact for most transactions, as compared to FIFO.

How does this method work? As a general principle, realizing taxable losses instead of gains and allowing short-term gains to mature into long-term gains (which are generally taxed at a lower rate) whenever possible should result in a lower tax liability in the long run. Instead of looking solely at the purchase date of each lot, TaxMin also considers the cost basis of the lot, with the goal of realizing losses before any gains, regardless of when the shares were bought. Lots are evaluated to be sold in the following order:

  1. Short-term losses
  2. Long-term losses
  3. Long-term gains
  4. Short-term gains

Generally, we sell shares in a way that is intended to prioritize generating short term capital losses, then long term capital losses, followed by long term capital gains and then lastly, short term capital gains. The algorithm looks through each category before moving to the next, but within each category, lots with the highest cost basis are targeted first. With a gain, the higher the basis, the smaller the gain, which results in a lower tax burden. In the case of a loss, the opposite is true: the higher the basis, the bigger the loss (which can be beneficial, since losses can be used to offset gains).1

A simple example

If you owned the following lots of the same security, one share each, and wanted to sell one share on July 1, 2021 at the price of $105 per share, you would realize $10 of long term capital gains if you used FIFO. With TaxMin, the same trade would instead realize a $16 short term loss. If you had to sell two shares, FIFO would get you a net $5 long term gain, while TaxMin would result in a $31 short term loss. To be clear, you pay taxes on gains, while losses can help reduce your bill.

Purchase Price ($) Purchase Date Gain or Loss ($) FIFO Selling order TaxMin Selling order
$95 1/1/20 +10 1 4
$110 6/1/20 -5 2 3
$120 1/1/21 -15 3 2
$100 2/1/21 +5 4 5
$121 3/1/21 -16 5 1

What can you expect?

TaxMin automatically works to reduce the tax impact of your investment transactions in a variety of circumstances. Depending on the transaction, the tax-efficiency of various tax-lot selection approaches may vary based on the individual’s specific circumstances (including, but not limited to, tax bracket and presence of other gains or losses.) However, we feel that TaxMin serves the typical Betterment customer far better than FIFO, the default used by most brokers.

Note that Betterment is not a tax advisor and your actual tax outcome will depend on your specific tax circumstances—consult a tax advisor for licensed advice specific to your financial situation.

This is just one more way we continue to innovate under the hood to maximize your investor returns: net of transaction costs, net of behavior, and net of tax.

1 Note that when a customer makes a change resulting in the sale of the entirety of a particular holding in a taxable account (such as a full withdrawal or certain portfolio strategy changes), tax minimization may not apply because all lots will be sold in the transaction.