The arithmetic is the easy part. The important work is identifying the day type, direction, boundary rule, and any calendar that overrides the general baseline.
Read the wording literally
“Within 14 calendar days” normally advances through every date, including weekends. “Within 10 business days” usually skips weekends and may also exclude specified holidays. “From” and “after” can affect whether the starting date counts. Copy these words into a short calculation note before entering numbers so that the result can be reviewed.
Separate the calculation from exceptions
First calculate under the stated calendar or Monday-to-Friday rule. Then inspect holidays, cutoff times, time zones, or special service terms that the general tool does not model. Keeping the steps separate makes it clear which part came from java.time arithmetic and which part came from an external authority.
Keep the inputs with the deadline
Record the start date, direction, amount, day type, boundary choices, and any external holiday source. A naked date is hard to audit later. DayCount does not save calculations, so copy the stated rule into the document or task where the deadline matters. Recalculate if the governing calendar or wording changes.