How to use the Countdown Calculator (Days Until)
- Under Countdown, pick a target date such as an exam or a trip. The days left from today appear as D-n.
- If you pick a date that has already passed, the days since then appear as D+n. To count that first day as Day 1, the way couples count from their first date, check "count that day as Day 1."
- Type a name and press Save to keep several countdowns in one list. The list is stored in this browser.
- Under Anniversary dates, pick a start date. A table shows each milestone from 50 to 3,000 days, plus the 1st to 10th yearly anniversaries, with the date, the weekday and the days left.
How a countdown (D-day) is calculated
A countdown counts the days remaining until a target date. The target date itself is D-Day. The day before is D-1 and the day after is D+1.
Days left = target date − today
For example, if today is March 1 and your exam is on March 31, then 31 − 1 = 30, so it's D-30. To count the days left including today, add 1 to the result (30 days + today = 31 days).
Counting 100 days: the start date is Day 1
Couples who celebrate relationship milestones usually count the day they got together as Day 1. That means Day 100 falls 99 days after the start date.
| Start date | 100 days | 200 days | 1000 days |
|---|---|---|---|
| Jan 1, 2026 | Apr 10, 2026 | Jul 19, 2026 | Sep 26, 2028 |
| May 5, 2026 | Aug 12, 2026 | Nov 20, 2026 | Jan 28, 2029 |
A baby's "100 days" milestone is often counted the same way, with the birth date as Day 1. Some counts start the day after an event instead, such as days sober, days on the job or days since you quit smoking. For those, choose the "Start date = Day 0" method.
Why "days left" and the D-number can differ by one
People often get confused when a countdown number and "how many days to go" differ by one. It all depends on whether you count today.
| Today → target | Countdown | Days left including today | Days left excluding today |
|---|---|---|---|
| Oct 1 → Oct 10 | D-9 | 10 days | 9 days (including the target day) |
| Oct 1 → Oct 2 | D-1 | 2 days | 1 day |
The D-number is the same as "how many sleeps until the big day." If you're splitting daily tasks starting today, such as packing for a trip, plan with the count that includes today (D-number + 1). That way you won't end up a day short.
Tips for exam and event countdowns
- Save your exam date, such as finals, the SAT, A-levels or the bar exam, and you'll see the days left every time you open Tooljip. Tap the favorite star (☆) to pin the tool to the first row of the home page.
- Splitting the days left into weeks makes a study plan easier. For example, D-84 is exactly 12 weeks.
- To find the number of weekdays between two dates, or the gap in months and days, use the date calculator.
- A to-do list helps you organize today's tasks, and a Pomodoro timer helps you manage study time.