This is one of the central questions confronting investors putting together their portfolios, yet there seems to be no consensus. Some experts argue for highly globalized portfolios, with allocations to foreign and U.S. stocks and bonds mirroring their market values. But other experts believe that due to the extra costs and volatility that can accompany foreign stocks and bonds-and especially the foreign-currency swings that can occur when those market gains or losses are translated into U.S. dollars-less is more when it comes to foreign exposure. A related question is whether (and how) a portfolio's allocations to foreign and U.S. stocks and bonds should change over time.

Stock Allocations: Fully Global, U.S.-Centric, or Somewhere In-Between?

 The issue of how much investors should stake in foreign stocks has been a contentious one for years. In the "less foreign is more" camp are experts who believe that because many U.S. blue chips are increasingly global in their reach, investors in them get exposure to foreign markets indirectly, while avoiding the extra costs and volatility associated with foreign stocks (foreign-currency swings in particular). At the other extreme are the "global market-cap agnostics"-those who suggest buying a basket of U.S. and foreign equities weighted according to their market values. The U.S./foreign allocations of global-market indexes have hovered around 50/50 for the past several years.

Meanwhile, most asset-allocation experts recommend a middle ground. Investors may not need to steer half of their portfolios to foreign stocks to obtain most of their diversification benefits. The rationale behind how much foreign exposure an investor may choose gets back to volatility. Because foreign stocks typically entail some currency risk as gains or losses are translated from foreign currencies to dollars, investors who want to reduce volatility may want to also reduce their foreign weightings accordingly.

Bonds: It's Complicated

Even though more than 50% of the world's fixed-income investments exist outside the United States, investing in foreign bonds has the potential to add cost and volatility to a U.S. investor's portfolio. Few asset-allocation experts are in favor of mirroring the global markets' allocation to U.S. and foreign bonds.

Because types of foreign-debt exposure vary so widely, one-size-fits-all recommendations are tricky. Investors could steer a larger share of their fixed-income portfolio to foreign sovereign bonds rather than corporate and/or local-currency-denominated debt.

The standard sequence for a tax-efficient portfolio drawdown is required minimum distributions first. Taxable accounts next, followed by Traditional IRAs and 401(k)s. Roth IRAs and 401(k)s last. The overarching thesis is to be sure to tap those accounts where you'll face a tax penalty for not doing so (RMDs) while hanging on to the benefits of tax-sheltered vehicles for as long as possible. Because Roth assets enjoy the biggest tax benefits--tax-free compounding and withdrawals--and may also be the most advantageous for heirs to receive upon your death, they generally go last in the withdrawal-sequencing queue.

That's a helpful starting point for sequencing retirement-portfolio withdrawals, and it goes without saying that you should always take your RMDs on time. That said it may be a mistake to always follow this strategy. The reason is that your tax picture will change from year to year based on your expenses, your available deductions, your investment performance, and your RMDs.

In order to keep your total tax outlay down during your retirement years, it may be worthwhile to maintain holdings in the three major tax categories throughout retirement: taxable, tax-deferred, and Roth. Armed with exposure to investments with those three types of tax treatment, retirees can consider withdrawal sequencing on a year-by-year basis, staying flexible about where they draw their income bases on their tax picture at large. They can help limit the pain of an otherwise high-tax year by favoring taxable and Roth distributions, for example, while giving preference to tax-deferred distributions in lower-tax years.

For example, in a year in which they have high medical deductions that push them into a lower tax bracket, they might actually give preference to withdrawals from their Traditional IRA accounts, even though they have plenty of taxable assets on hand, too. The reason is that it may be preferable to take the tax hit associated with that distribution when they're paying the lowest possible rate on that distribution. Moreover, aggressively tapping tax-deferred accounts like Traditional IRAs in low-tax years will mean that fewer assets will be left behind to be subject to RMDs.

On the flip side, in a high-tax year--for example, when RMDs are bigger than usual due to market appreciation--a retiree might reasonably turn to her Roth accounts for any additional income needed. Although those Roth assets usually go in the "save for later" column under the standard rules of withdrawal sequencing, those tax-free Roth withdrawals (versus, say, paying capital gains on distributions from a taxable account or paying ordinary income tax on tax-deferred withdrawals) may help the retiree avoid getting pushed into a higher tax bracket than would otherwise be the case.

401(k) plans are long-term retirement savings vehicles. Withdrawal of pre-tax contributions and/or earnings will be subject to ordinary income tax and, if taken prior to age 59 1/2, may be subject to a 10% federal tax penalty. Funds in a traditional IRA grow tax-deferred and are taxed at ordinary income tax rates when withdrawn. Contributions to a Roth IRA are not tax-deductible, but funds grow tax-free, and can be withdrawn tax free if assets are held for five years. A 10% federal tax penalty may apply for withdrawals prior to age 59 1/2.