On the day of your birth, have an actuary calculate your life expectancy to (say) 3 decimal digits, which is enough precision to nail down the expected month, day, and year of your death. This is similar in spirit to an astrologer, on the day of a baby's birth, drawing up a chart predicting the baby's future, except actuarial calculations of life expectancy are real. (Though maybe the astrologer subconsciously ignores the planets and stars and also reports a subconscious actuarial calculation.)
Then, celebrate that month and day each year as a numbered negative anniversary of the day of your death.
Of course, you may wish to try to outlive that date.
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