Medical expenses increase unpredictably with age, so the crystal ball gets very hazy when trying to foretell how much you’ll need in retirement. A new study helps clear things up: a single older American spends about $39,000 on average for medical care in the final five years of life, or about $7,800 a year. For couples in which one spouse has died, $51,000 was spent during that spouse’s final years, or about $10,000 annually. These out-of-pocket expenses, which were reported by surviving spouses and family members, are for health care not covered by Medicare: insurance premiums, hospital and physician copayments and deductibles, and expenses for medications, nursing homes, and in-home care. The data also show that the financial burden on…