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Instead of a gradual decline, your portfolio could spiral downward rapidly, leaving little time for course correction. A new tool, the "momentum ratio," can help gauge your portfolio's vulnerability. This ratio compares positive and negative returns over time, signaling potential trouble if it exceeds certain thresholds.

Even seemingly small market losses early in retirement can have a long-term impact. The good news? Financial advisors can play a critical role by monitoring your portfolio regularly and helping you adjust withdrawals to prevent your savings from entering the "death spiral."