You might want to reschedule your dog's birthday party.

That is, if you care about celebrating it on the correct day. According to a new study, it doesn't really make sense to calculate a dog's age the traditional way — by multiplying its "human year" age by seven.

The actual formula, it turns out, might mean breaking out your graphing calculator.

Researchers from the University of California San Diego published the new calculation earlier this month, based on an experiment that looked at more than 100 Labrador retrievers between the "human" ages of four weeks and 16 years.

So what's the magic equation? To find out your dog's "real" age, you need to find the natural logarithm of your dog's current age (that's where the calculator comes in handy), then multiply that number by 16 and add 31. Here's what it looks like written out:

**16 x ln( the natural logarithm of your dog’s age in "human years") + 31**

Confused? Here's an example. Say you have a 4-year-old Labrador named Comet — with the new equation, Comet's real "dog age" would be slightly older than 53.

The reason for the difference is actually pretty simple. Even though dogs experience similar life stages to humans, they tend to age at different rates depending on how old they are. Dogs typically age faster than humans when they're younger, and that process begins to slow down as they get older, according to the study.

Popular Mechanics reported that the researchers hope to expand their study to include more dog species, as there may be some differences among breeds. In the meantime, though, you'll just have to rely on this more accurate — if not headache-inducingly complex — way for planning your pet's next birthday party.