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Updated April 23, 2011 12:01 a.m. ET

Most portfolios are managed for an event on a distant horizon, say retirement or a child’s college education. But some tools and strategies most commonly used for core holdings also can sharpen the discretionary or tactical portion of your portfolio.

Sites like MyPlanIQ (www.myplaniq.com ), MarketRiders (www.marketriders.com ) and MoneyChimp (www.moneychimp.com ) provide you with tools, data and the instructions needed to assemble stock and fund portfolios designed to minimize risk and maximize return.

MyPlanIQ offers both longer-term strategic and shorter-term tactical asset-allocation recommendations based on literally thousands of plans used by registered money managers. The plans can range from actual 401(k)s in place at companies like Ford Motor and General Electric to those advocated by brokers like Charles Schwab or Fidelity to those offered by well-known financial gurus like Yale professor Robert Shiller. After assessing his risk profile, the investor can choose to follow one of these plans or one assembled by MyPlanIQ, which has developed its own algorithms.

They all share the belief that good asset allocation brings the best returns. Studies have shown asset allocation to be responsible for as much as 90% of the typical portfolio’s return, notes MyPlanIQ’s president, Simon Napper. Instead of picking stocks one by one, this approach suggests buying a portfolio’s worth at a time.

Generally, potential return is proportional to the risk accepted. But Modern Portfolio Theory posits that some securities, sector or market risks can be avoided or offset by holding noncorrelated assets. When one asset class is down, others are likely to be up, according to this widely followed thesis. Like a growing number of advisors, MyPlanIQ recommends using low-cost exchange-traded funds as diversified proxies for asset classes. The firm’s Strategic Asset Allocation models are geared to a long investing horizon.

For midcourse corrections, MyPlanIQ relies on a different set of academic studies to build Tactical Asset Allocation models. Essentially, these tactical allocations rebalance portfolios periodically based on momentum factors like asset price moves relative to its market benchmark. True momentum investing is more multifaceted (The Electronic Investor, Where to Gather Momentum , March 21). But tactical shifts can mitigate some short-term risks that asset diversification alone doesn’t address, says Napper.

For example, in the summer of 2008, prior to the October crash, MyPlanIQ’s algorithm began sending out alerts suggesting that its tactical portfolios go to cash. Its longer-term strategic models, meanwhile, rode the market down to its March 2009 low (since rebounding with the market). Based on back-testing, MyPlanIQ’s strategic portfolios should produce an extra 1% return a year over major market indexes, Napper claims. His tactical models add 4% to 6% to the market return.

The average investor needs multiple profiles, he explains, because of his participation in a variety of vehicles like 401(k)s or Roth IRAs or standard mutual funds, among many others, each of which must comply with different government rules and tax requirements. Five portfolios should do it for most people, says Napper, and MyPlanIQ’s first five strategic asset-allocation models are free. A $10 monthly subscription is needed to tap the tactical aids or to build your own model from scratch.

MYPLANIQ SENDS e-mail alerts when it’s time to buy and sell shares to maintain asset-allocation percentages. Annual or semi-annual rebalancing should suffice for strategic portfolios. But more-actively traded portfolios need more frequent adjustment.

MarketRiders, another $10 monthly portfolio advisory service, offers a similar side bet to its Modern Portfolio Theory-based holdings. Whereas the typical retirement portfolio might have a 20-year horizon, investors need a way to respond to interim events, agrees CEO Mitch Tuchman.

MarketRiders’ first tactical portfolio seeks to hedge the effects of high energy prices on subscribers’ net worth–their portfolios in a larger sense. The Energy Hedge Portfolio includes six cost-effective ETFs that represent the major divisions of the energy sector for a weighted-average fund fee of about 0.5% (www.marketriders.com/energy-hedge-portfolio ). Instead of trying to guess individual energy winners, subscribers gain exposure to top companies in each of the sector’s major groups.

Six appears to be the optimum number of asset types needed to diversify a portfolio without running up too many costs, says Napper. MyPlanIQ’s Six Core Asset portfolio uses sectorwide ETFs representing U.S. international and emerging-market equities, real estate, commodities and bonds–a number even the busiest investor can follow.

Lazy investors can get along with still fewer positions, insist contributors to the Bogleheads Wiki (www.bogleheads.org/wiki/Lazy_Portfolios ), the online clubhouse for devotees of Vanguard Group Founder John Bogle (https://personal.vanguard.com/us/home ). Several Bogleheads have posted lazy portfolios with as few as three or four broad market funds that, the site maintains, perform well under most market conditions. Lazy portfolios are, typically, 30% to 40% in bonds and favor low-cost Vanguard funds to minimize rebalancing and, thus, brokerage costs and taxes.

Most have beaten the S&P 500 Index every year back to 2002, says columnist Paul B. Farrell, who tracks eight such lazy portfolios for Barron’s affiliate MarketWatch (www.marketwatch.com/lazyportfolio ). The Lazy Portfolio page includes Farrell’s columns, free e-mail news alerts and step-by-step instructions for building your own simple-but-diversified portfolio.

sporkforge.com ) and Investopedia (www.investopedia.com ). These sites have reams of information on the nuts and bolts of risk versus reward.

Sure, it’s rocket science, but you don’t need a Ph.D. to own a rocket. Even lazy investors will find the prebuilt portfolios on MyPlanIQ and MarketRiders easy to use or even customize. Their systems are slicker than the Boglehead recommendations, but these sites are still just combining different amounts of common sense with well-publicized lessons learned by influential money managers. Tuchman has been surprised at how many people are using his tools to build their own.

I guess a certain percentage of people, like Barron’s readers, he says, just love this stuff.