I recently chatted with a retired couple who were looking for a second opinion about their portfolio's asset allocation. The key question: Is 65% in stocks too high for someone in their situation? Here, I'll walk through some ideas about how to think through these issues.

Jot down what your spending looks like in a typical month, including costs for housing, food, medical care, insurance, clothing, charitable donations, and taxes. Then you can add in discretionary spending, such as travel, entertainment, major purchases, and the like.

If you're working with a financial advisor, he or she should be able to use this data to estimate your lifetime spending needs. If you're managing your own assets, you can do a rough calculation by reverse engineering the 4% rule: Multiply your planned annual spending by the inverse of the withdrawal percentage; for example, someone who plans to spend $50,000 per year would need a portfolio of at least $1.4 million ($50,000 times 28.6, which is the inverse of 3.5%).

Next, it's time to think about asset allocation for these core assets.

If you want to prioritize leaving assets (bequests) to charity or family members, you might be comfortable with a higher equity allocation, which should allow for continued growth while the assets are still in your portfolio.

Investors who aren't as focused on asset growth for eventual bequests to charity or family members might be more comfortable prioritizing safety instead, and can tilt their "extra" portfolio towards bonds.

Of course, these two scenarios are just a starting point. A couple in this situation might end up deciding on a portfolio allocation somewhere in between, or decide to carve out additional buckets, such as a separate bucket for charitable donations during their lifetime or another bucket for "fun money" to enjoy the fruits of a lifetime of work and saving.

Even for investors comfortable with a higher equity allocation, it's prudent to reduce exposure to individual stocks if they're significantly overvalued or consume a large percentage of the portfolio (5% or more is a rough guideline).

It's also worth considering whether each spouse has the same level of risk tolerance and comfort with investing. Think about how a surviving spouse might handle remaining assets and make sure the portfolio's asset mix is something both members of the couple are comfortable with for the long term.

At the end of the day, there's no "right" answer to creating an asset-allocation mix. It all comes down to an individual's level of risk tolerance, portfolio size, and anticipated spending needs. But investors who have enough assets to cover their planned spending during retirement--and then some--have more flexibility to create a customized asset mix that reflects their goals and priorities.