Taxation of capital gains upon accrual: is it really more efficient than realisation?

Taxation of capital gains upon realisation is known to discourage the liquidation of an appreciated asset (lockin effect), thus resulting in a distortion in portfolio choices. However, compared with taxation upon accrual, realisation-based taxation may imply a lower distortion in intertemporal allocation of consumption. In particular, we show that this is always the case when preferences are intertemporally weakly separable and homothetic. Using a simple model of intertemporal choice, we assess and compare the distortions induced by the two tax regimes of accrualbased and realisation-based taxation of capital gains. Our numerical simulations show that, for reasonable values of the parameters, realisation-based taxation can in fact imply a lower overall distortion of investment choices, and hence no clear ranking of the two systems is possible in general. Additionally, we find that the differences in efficiency, in either direction, are likely to be very small.