How this calculator works
The calculator subtracts date-only values on a UTC calendar, so daylight-saving changes do not add or remove a day. The start date is day zero and the next date completes one day. Weeks have seven days. Calendar years and months are counted by anniversaries, clamping a start day such as the 31st to the last valid day of a shorter month. This is a personal date tracker; a date total is not a clinical measure of recovery or a judgement of progress. The result is an estimate for information only and is not medical advice.
Formula
Completed days = end date minus start date, measured in calendar days. Milestone date = start date + requested days. Start date = as-of date - completed days.
Worked example
From 2024-02-28 to 2024-03-01 is 2 days because 2024 has a leap day. A 100-day milestone from 2026-01-01 falls on 2026-04-11.
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Frequently asked questions
Is my first date counted as day one?
This tool counts elapsed days, so it reports zero on the start date. Some people label that day day one; that is a different counting convention.
Does the result update itself tomorrow?
The as-of date is explicit and saved with your inputs. Change it to the date you want to measure.
Why can a month mean different numbers of days?
Calendar months have 28 to 31 days. The calendar breakdown uses actual anniversaries, while completed days remain an exact date difference.