Date Between Formula:
dateBetween(prop("Due Date"), now(), "days")

Concat String Formula:
concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Overdue")

Negative Check on Formula: 
if(dateBetween(prop("Due Date"), now(), "days") < 0, concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Left"), concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Overdue"))

Negative Replacement Formula:
if(dateBetween(prop("Due Date"), now(), "days") < 0, replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Left"),"-", ""), replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Overdue"), "-", ""))

S Replacement Formula: 
if(dateBetween(prop("Due Date"), now(), "days") < 0, replace(replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Left"), "-", ""), "1 Days", "1 Day"), replace(replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Overdue"), "-", ""), "1 Days", "1 Day"))

Optimized S Replacement Formula:
replace(if(dateBetween(prop("Due Date"), now(), "days") < 0, replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Left"), "-", ""), replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Overdue"), "-", "")), "1 Days", "1 Day")

Switch Negatives:
replace(if(dateBetween(prop("Due Date"), now(), "days") > 0, replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Left"), "-", ""), replace(concat(format(dateBetween(prop("Due Date"), now(), "days")), " Days Overdue"), "-", "")), "1 Days", "1 Day")

Empty Date Formula:

Final Formula:
if(toNumber(prop("Due Date")) == toNumber(""), "", if(if(dateBetween(prop("Due Date"), now(), "days") > -1, dateBetween(prop("Due Date"), now(), "days") + 1, dateBetween(prop("Due Date"), now(), "days")) > 0, replace(concat(format(if(dateBetween(prop("Due Date"), now(), "days") > -1, dateBetween(prop("Due Date"), now(), "days") + 1, dateBetween(prop("Due Date"), now(), "days"))), " Days Left"), "1 Days", "1 Day"), replace(concat(format(if(dateBetween(now(), prop("Due Date"), "days") > -1, dateBetween(now(), prop("Due Date"), "days"), dateBetween(now(), prop("Due Date"), "days"))), " Days Overdue"), "1 Days", "1 Day")))

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