Realization and Lock-In When Interest Rates are Low

5 Pages Posted: 11 Sep 2016

Date Written: August 22, 2016


This article uses simple numerical examples to study the relationship between interest rates and the familiar problem of "lock-in" that arises from deferred taxation of unrealized appreciation. In the cases we study, lock-in comes about because of positive taxpayer borrowing costs, and realization and deferral remain significant problems for income taxation even in periods of low government borrowing rates.

We also find that it is the relative size, rather than the absolute size, of the borrowing costs that matters. Specifically, lock-in prevents a taxpayer from selling an asset and buying another with a higher pre-tax return only when the incremental after-tax return increase is greater than the borrowing cost necessary to pay the tax triggered as a result of the sale. Thus the magnitude of the lock-in problem does not necessarily diminish as borrowing costs fall, but rather it depends upon a complex relationship between and among the falling interest rates, the incremental increased returns that are available, and the amount of unrealized appreciation in assets.

Keywords: lock-in, tax deferral, realization requirement, interest rates, borrowing costs

JEL Classification: H24, K34

Suggested Citation

Brennan, Thomas J. and Warren, Alvin C., Realization and Lock-In When Interest Rates are Low (August 22, 2016). Tax Notes, Vol. 152, No. 8, 2016, Available at SSRN:

Thomas J. Brennan (Contact Author)

Harvard Law School ( email )

1557 Massachusetts Ave
6 Ever
Cambridge, MA 02138
United States
617-495-3141 (Phone)

Alvin C. Warren

Harvard Law School ( email )

1575 Massachusetts
Hauser Hall 308
Cambridge, MA 02138
United States

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