Cost Basis (Tax Basis)

Cost basis, also called tax basis, is the original value of an asset for tax purposes, usually the purchase price adjusted over time for items such as improvements, fees, reinvested distributions, and corporate actions. When the asset is sold, the taxable gain or loss is the difference between the sale proceeds and the basis, which makes basis records as financially significant as the records of the assets themselves.

The concept exists in most tax systems, but the detailed rules are jurisdiction-specific. In the United States, basis is adjusted upward for capital improvements and certain reinvestments, downward for depreciation, and reset for inherited assets, which generally receive a new basis equal to their value at the owner's death, a rule known as the step-up.

Why it matters for family offices

Families that hold assets for decades feel basis rules more than most investors. A single position may carry dozens of tax lots bought at different times and prices, and choosing which lots to sell can meaningfully change the tax outcome of the same economic decision. Transfers between generations complicate matters further: in the United States, gifted assets generally carry the giver's basis, while inherited assets are stepped up, so how an asset passes within a family changes the tax character of the gain embedded in it. None of this can be managed after the fact if the records are missing.

How it shows up in practice

The classic family office problem is reconstruction. An office consolidating a family's holdings discovers a stock position accumulated over thirty years across three custodians, two of which no longer exist, with dividends reinvested throughout. Establishing a defensible basis means assembling old statements, corporate action histories, and transfer records, sometimes over months. Offices that record basis at the moment each asset is acquired, and carry it through every transfer between accounts and entities, avoid this entirely. It is one of the strongest arguments for systematic record-keeping over scattered statements: basis is easy to capture at purchase and painful to rebuild decades later.