Cost Basis vs Market Value: Track Investment Gains

An investment account balance tells you what your holdings are worth now. It does not, by itself, tell you how much you contributed or how well those investments performed.

To understand the difference, start with two figures: cost basis and market value. Keeping them separate helps you read account statements, maintain useful records and avoid mistaking new deposits for investment gains.

This guide is educational, not personalised financial, investment, tax or legal advice. Investments can lose value. Consult a qualified professional for guidance on your own situation, particularly when working out tax reporting requirements.

What is cost basis?

For simple personal tracking, cost basis starts with the amount you paid to acquire an investment. Certain purchase costs may also be included, depending on the purpose of the calculation and applicable rules.

Suppose you purchase 10 ETF units for 40 currency units each and pay a purchase fee of 5. Your total acquisition outlay is:

(10 × 40) + 5 = 405

For an everyday tracking record, 405 gives you a useful starting point for comparing that purchase with its later value.

Tax cost basis is a separate matter. Its calculation can depend on local rules, account type, acquisition method and later adjustments. Inherited or gifted assets, corporate actions and certain distributions can require different treatment. Do not assume a simple purchase-cost record is automatically suitable for a tax return.

What is market value?

Market value estimates what your investment is worth at a particular time.

For a regularly traded asset, the basic calculation is:

Market value = quantity owned × price per unit

If those 10 ETF units are quoted at 46 each, their market value is 460. Their original acquisition outlay remains 405 unless an adjustment is needed.

Market value is the figure generally relevant to a current net worth snapshot. Cost basis provides historical context; it is not an additional asset to add to that snapshot.

A quoted value is not necessarily the cash you would receive from a sale. Trading costs, spreads, market movements and other charges may reduce the proceeds. For less frequently traded assets, the valuation may also be uncertain or out of date.

Calculate a simple unrealised gain or loss

An unrealised gain or loss is a change in value on an investment you still own.

For a straightforward purchase with no later adjustments:

Unrealised gain or loss = current market value − cost basis

Using the example above:

• Acquisition outlay used as the tracking basis: 405
• Current market value: 460
• Unrealised gain: 55

A simple percentage comparison is:

Unrealised gain percentage = gain ÷ cost basis × 100

Here, 55 ÷ 405 × 100 is approximately 13.6%.

This is not an annual return. It also excludes distributions, ongoing costs not included in the calculation and any potential sale costs or taxes. Label it clearly as an unrealised price gain relative to your recorded basis, rather than your complete investment return.

Understand what changes when an asset is sold

A realised gain or loss arises when you dispose of an investment. For a simple tracking calculation, compare net sale proceeds with the cost basis assigned to the units sold.

Suppose all 10 units sell for 460, with a sale fee of 5:

Net proceeds = 460 − 5 = 455

Realised gain = 455 − 405 = 50

The gain is smaller than the earlier unrealised figure because the sale cost reduces the proceeds.

A realised gain is not necessarily the same as a taxable gain. Tax treatment can vary, and some transactions other than sales may also create reporting obligations. Keep transaction records rather than relying only on a portfolio summary.

Keep separate records for repeated purchases

Buying the same investment more than once creates separate acquisition records, often called lots.

Imagine these purchases, ignoring fees:

• 5 units at 20 each: cost of 100
• 5 units at 30 each: cost of 150
• Total: 10 units costing 250

If the current price is 28, the combined market value is 280 and the overall unrealised gain is 30.

If you later sell only some units, the basis assigned to those units matters. Different jurisdictions and account arrangements may require or permit different identification or averaging methods.

For reliable records, retain each purchase date, quantity, price and fee. A displayed average purchase price can be useful, but it should not replace the underlying transaction history.

Separate investment income from price changes

Price gains are only one part of investment performance. Some assets also generate income, such as dividends or bond interest.

Suppose an investment costs 1,000, later has a market value of 1,020 and pays a cash distribution of 30. Its price gain is 20. Its combined price change and cash income is 50, before any other relevant costs or taxes.

If the distribution is reinvested, record both events:

1. Income was received.
2. That money acquired additional units.

Otherwise, the additional units may look like unexplained growth or a fresh contribution from your own pocket.

Distribution treatment can be more complicated than this example. Retain provider statements showing how payments are classified and whether basis adjustments are required.

Do not confuse deposits with investment returns

An account can grow even while its investments lose value.

For example:

• Opening account value: 2,000
• New money deposited: 500
• Closing account value: 2,400

The balance rose by 400, but after allowing for the deposit, the account is down 100.

A useful account-level reconciliation is:

Investment result = closing value − opening value − external contributions + external withdrawals

This measures an absolute result over the period, assuming the records capture all relevant flows. It is not a percentage return adjusted for when deposits or withdrawals occurred.

Define the tracking boundary first. Moving assets between two accounts you include in the same portfolio is an internal transfer, not a new contribution to that portfolio. Preserve acquisition records when assets move.

Adapt your records to the asset

The same distinction between historical cost and current value applies across asset types, but valuation details differ:

• Stocks and ETFs: Record quantities, purchase costs, distributions and corporate actions.
• Bonds: Distinguish purchase cost, current value and principal due at maturity. Check whether a quoted valuation includes accrued interest.
• Gold and silver: Record weight, purity, purchase premiums and fees. A reference metal price may differ from a dealer's purchase offer.
• Crypto: Keep quantities, transaction fees and transfer records. Transfers between your own wallets should not appear as new contributions in a combined portfolio record.

Use consistent valuation dates and label estimates. Precision in a spreadsheet cannot make an uncertain sale price certain.

Track it in one place

Ledgerol is a net worth tracking app covering bank accounts, cash, stocks and ETFs, bonds, precious metals, commodities and crypto. Use a consolidated view to keep current wealth in perspective, while retaining detailed acquisition and transaction records separately. Market value answers what you own is worth now; cost basis helps explain how that value compares with its recorded cost.