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Quick Answer
What is Sunday − 78 days?
These sentences all describe the same result:
If today is Sunday, 78 days before was Saturday
78 days before Sunday is Saturday
Sunday − 78 days = Saturday
The weekday 78 days before Sunday is Saturday
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 Sunday and count backward 1 step(s).
| Step | Weekday |
|---|---|
| 0 | Sunday (start) |
| 1 | Saturday (result) |
Quick Lookup Table
Common values going backward from Sunday.
| Days before Sunday | Weekday | Remainder (mod 7) |
|---|---|---|
| 0 | Sunday | 0 |
| 1 | Saturday | 1 |
| 2 | Friday | 2 |
| 3 | Thursday | 3 |
| 4 | Wednesday | 4 |
| 5 | Tuesday | 5 |
| 6 | Monday | 6 |
| 7 | Sunday | 0 |
| 8 | Saturday | 1 |
| 9 | Friday | 2 |
| 10 | Thursday | 3 |
| 14 | Sunday | 0 |
| 21 | Sunday | 0 |
| 28 | Sunday | 0 |
| 30 | Friday | 2 |
| 78 | Saturday | 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.