Cookbooks
Lua
Chapter 7. Dates and Times
Calculating a date in the future or past

Lua:
Calculating a date in the future or past

How to:

In Lua, you have the os.date and os.time functions at your disposal to help with date and time calculations.

-- Add days to the current date
local daysToAdd = 10
local futureDate = os.time() + (daysToAdd * 24 * 60 * 60) -- days * hours * minutes * seconds
print("Future Date: " .. os.date("%Y-%m-%d", futureDate))

-- Subtract days from the current date
local daysToSubtract = 5
local pastDate = os.time() - (daysToSubtract * 24 * 60 * 60) -- same conversion as above
print("Past Date: " .. os.date("%Y-%m-%d", pastDate))

Sample output might be:

Future Date: 2023-05-03
Past Date: 2023-04-18

Deep Dive

Lua’s os.date and os.time functions have their roots in the standard C library. This means they’re close to the metal — efficient and reliable. They don’t fancy stuff like time zones or daylight savings time; they deal in UTC and seconds since the Unix epoch (January 1, 1970).

Alternatives to os.date and os.time exist if you’re looking for more. Libraries like Luadate offer more sophisticated operations, handling time zones and daylight savings with more finesse.

When it comes to implementation, keep an eye on leap seconds, and remember that adding a month isn’t as simple as adding 30 days. Different months have different day counts, and February can either shortchange or surprise you with an extra day.

See Also

For a more luxurious date and time experience in Lua, check out these resources:

Comparing two dates