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Quick Answer
What is Tuesday − 78 days?
These sentences all describe the same result:
If today is Tuesday, 78 days before was Monday
78 days before Tuesday is Monday
Tuesday − 78 days = Monday
The weekday 78 days before Tuesday is Monday
Detailed Math (Step-by-Step)
We show the whole operation clearly (modulo 7).
Step 1: Find the remainder
Since weekdays repeat every 7 days: days mod 7 tells us how many steps to move backward.
| Days | 78 |
|---|---|
| Divide by 7 | 11 remainder 1 |
| Remainder | 1 |
Step 2: Move backward 1 day(s)
Start at Tuesday and count backward 1 step(s).
| Step | Weekday |
|---|---|
| 0 | Tuesday (start) |
| 1 | Monday (result) |
Quick Lookup Table
Common values going backward from Tuesday.
| Days before Tuesday | Weekday | Remainder (mod 7) |
|---|---|---|
| 0 | Tuesday | 0 |
| 1 | Monday | 1 |
| 2 | Sunday | 2 |
| 3 | Saturday | 3 |
| 4 | Friday | 4 |
| 5 | Thursday | 5 |
| 6 | Wednesday | 6 |
| 7 | Tuesday | 0 |
| 8 | Monday | 1 |
| 9 | Sunday | 2 |
| 10 | Saturday | 3 |
| 14 | Tuesday | 0 |
| 21 | Tuesday | 0 |
| 28 | Tuesday | 0 |
| 30 | Sunday | 2 |
| 78 | Monday | 1 |
Tip: Any number of days that differs by a multiple of 7 lands on the same weekday.
Instant Calculator
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More “Weekday Before” Examples
Check other weekday calculations going backward in time.