Formulas to copy
With the start date in A1 and the target in B1 (Excel and Google Sheets):
| You want | Formula |
|---|---|
| Days until the target | =B1-TODAY() |
| Days since the start | =TODAY()-A1 |
| Day number (start = day 1) | =TODAY()-A1+1 |
| 100th-day date (start = day 1) | =A1+99 |
| End of an 18-month term | =EDATE(A1,18)-1 |
| Business days between (both ends) | =NETWORKDAYS(A1,B1,holidays) |
If a result looks like a date when you wanted a number, change the cell format to Number, and the other way round.
Common mistakes
- Inclusive counting — milestones like the 100th day add one. Decide first: day number vs days since.
- Adding months as 30 days — use EDATE; months have different lengths.
- DATEDIF with “MD” — Microsoft’s own documentation warns that the MD argument can give inaccurate results. Use subtraction for day counts.
- TODAY() changes every time the file opens — paste as values to freeze a record.
Sheet vs calendar vs app
| Tool | Good at | Less good at |
|---|---|---|
| Spreadsheet | business days, many dates at once, tables | checking a number on your phone every day |
| Phone calendar | events and reminders together | often no visible “days left” number |
| Countdown app | days left at a glance, repeating anniversaries | no complex math like business days |
A practical split: calculate in the sheet, watch the number in the app.
Moving dates into the app
Enter the calculated date as the target
Put the date from your sheet (a 100th day, an expiry, a business-day deadline) into D-Day Counter as the Target Date and sort by Nearest.
Back up before changing phones
Settings has a Backup / Restore option that exports your countdowns to a file you can import on a new phone. The app has no account and stores data only on the device, so back up before you switch.
The app’s English screenshots below still show sample titles in Korean (an exam and a wedding anniversary).
FAQ
Do these formulas work in Google Sheets?
Yes, all of them use the same names in Google Sheets.
How do I count the weeks I have lived?
See how many weeks have I lived for week formulas and the 10,000-day date.
D-Day Counter · Days Until / Since
No sign-up: just a title and a date. Everything stays on your phone. Free on Android, in English and Korean.