Fortnight — Definition, Formula & Examples
A fortnight is a unit of time equal to exactly 14 days, or 2 weeks. The word comes from the Old English "fēowertyne niht," meaning "fourteen nights."
A fortnight is a standard time interval defined as a period of 14 consecutive days. It is equivalent to 2 weeks, 336 hours, 20,160 minutes, or 1,209,600 seconds. While rarely used in everyday American English, the fortnight remains a common unit in British, Australian, and other Commonwealth countries, particularly for pay schedules and scheduling contexts.
Key Formula
Where:
- = Total number of days
- = Number of fortnights
- = Days in one fortnight
How It Works
To use a fortnight in time calculations, remember the key fact: 1 fortnight = 14 days = 2 weeks. If someone says an event is "3 fortnights away," multiply 3 by 14 to get 42 days. To convert days into fortnights, divide the number of days by 14. A calendar year contains approximately 26 fortnights, since . Many workers in the UK and Australia are paid on a fortnightly basis, meaning they receive a paycheck every 2 weeks — resulting in 26 pay periods per year.
Worked Example
Problem: A summer camp lasts 5 fortnights. How many days and weeks is that?
Step 1: Write the conversion formula for fortnights to days.
Step 2: Substitute 5 for F.
Step 3: Convert 70 days to weeks by dividing by 7.
Answer: The summer camp lasts 70 days, which is 10 weeks.
Another Example
This example reverses the direction — converting days into fortnights — and involves a remainder, which is a common real-world situation.
Problem: A project deadline is 63 days from today. How many fortnights is that, and how many extra days remain?
Step 1: Divide the total days by 14 to find the number of complete fortnights.
Step 2: Verify by multiplying back and adding the remainder.
Step 3: Express the remainder in weeks: 7 days = 1 week.
Answer: 63 days is 4 fortnights and 1 week (or equivalently, 4 fortnights and 7 days).
Visualization
Why It Matters
Understanding the fortnight helps you work with time-unit conversions in elementary and middle school math. In countries like the UK and Australia, pay schedules, rent, and bills are often calculated on a fortnightly basis, making this unit practical for budgeting and financial literacy. It also appears in standardized math problems involving unit conversion and elapsed time.
Common Mistakes
Mistake: Thinking a fortnight is 15 days instead of 14
Correction: "Fortnight" comes from "fourteen nights" — it is always exactly 14 days, not 15. Remember: fort- sounds like "four-teen."
Mistake: Confusing a fortnight with a month
Correction: A fortnight is 14 days (2 weeks), while a month ranges from 28 to 31 days. A fortnight is always shorter than any calendar month.
Mistake: Forgetting the remainder when converting days to fortnights
Correction: Days don't always divide evenly by 14. For example, 30 days is 2 fortnights and 2 extra days, not simply 2 fortnights.
Check Your Understanding
How many hours are in 1 fortnight?
Hint: There are 24 hours in a day, and 14 days in a fortnight. Multiply 14 × 24.
Answer: 336 hours
If you save $5 every fortnight, how much do you save in a year (26 fortnights)?
Hint: Multiply $5 by 26.
Answer: $130
How many fortnights are in 84 days?
Hint: Divide 84 by 14.
Answer: 6 fortnights