Our own changing lives.

The biggest question mark for any of us comes from the unknowable future.

Will we change jobs? Earn more? Have kids? Help our adult children? Retire early because of our own choice, or choices made by employers who no longer want us around? These things matter so much more than any tax rules. Depending on how our lives change, any tax changes may help or hurt.

Changing tax rates over time.

When all of Washington is occupied with today’s proposed tax changes, it’s easy to forget that we’ve been here before and will be here again. Nearly every recent president has taken his shot at revising the system. And while the proposals here are potentially farther reaching, future politicians will make changes, too.

“In the back of my mind, I don’t anticipate taxes staying low for a long period of time,” said Julie Welch, an accountant and financial planner in Leawood, Kan.

After all, we’re adding to the national debt here in the hopes of stoking growth. If that doesn’t work, it won’t change the fact that Medicare and Medicaid will cost ever more money as the population ages. Something will have to give, and because Medicare is one of the most sacred cows of all, we’re more likely to raise taxes again than to make older people pay more for their health care.

Changing tax rules over time.

Our retirement accounts seem safe for now, though it wouldn’t be surprising to see the tax rules for 401(k)’s and similar workplace savings accounts back on the table next week or next year.

In the meantime, consider the possibilities. If more people keep saving in Roth retirement accounts of various sorts, where you don’t get a tax break when you put aside the money but it comes out free of income taxes after decades of appreciation, the balances will one day dwarf what sits in them today. And as they grow, legislators will be tempted to cap their size or to tax withdrawals.

This possibility has to be on the mind of any prudent financial planner working with younger clients who have the most time to save, given how often wholesale changes to Roth accounts have already come under consideration.