Contrary to what’s stated elsewhere, the elimination half-life of modafinil is about 15 hours. However, some sources quote the half-life as ~13 hours.

The half-life of a drug is the amount of time it takes for the body to eliminate 50% of the drug from plasma (e.g., the bloodstream).

The half-life of modafinil has been studied extensively, but the results have not been completely uniform. Here are three sources authoritative sources that are in the same ballpark.

Finding Study
12-15 hours Robertson P, Hellriegel ET. Clinical pharmacokinetic profile of modafinil. Clin Pharmacokinet. 2003;42(2):123-37.
13.6 hours Darwish M, Kirby M, Hellriegel ET, Robertson P. Armodafinil and modafinil have substantially different pharmacokinetic profiles despite having the same terminal half-lives: analysis of data from three randomized, single-dose, pharmacokinetic studies. Clin Drug Investig. 2009;29(9):613-23.
15 hours

Note that while the mean elimination half-life of modafinil’s sister drug armodafinil (Nuvigil) is roughly identical, it nevertheless has a greater AUC (area-under-the-curve) with monophasic pharmacokinetics.

See the following abstract1:

Armodafinil and modafinil both had a mean single-dose terminal elimina- tion half-life of ~13 hours, with similar mean maximum plasma drug concentration (Cmax) and median time to Cmax values. After reaching Cmax, plasma concentrations appeared to decline in a monophasic manner with armodafinil, but in a biphasic manner with modafinil due to the initial rapid elimination of its S-isomer. As a result, mean area under the plasma drug concentration versus time curve (AUC) from time zero to the time of the last measurable concentration (AUClast) and AUC from time zero to infinity (AUC¥) values were 33% and 40% higher, respectively, with armo- dafinil compared with modafinil on a milligram-to-milligram basis.

modafinil pharmacokinetics elimination half-life

How Long Does Provigil Stay In Your System?

This answer is tricky becuase it depends on how you define “stay in your system.”

After three half-lives, the remaining concentration of a drug is 12.5%. We’ll treat the drug as being essentially gone at this point, even though a small amount remains.

Since the half-life of modafinil is 15 hours, three half-lives is 45 hours (3 x 15 h) or almost 2 days. So how long does Provigil stay in your system? About 2 days.

How Long Does Modafinil Take to Kick In?

Great question!

The chart above that plots of pharmacokinetics of modafinil will help address this question. If you look at the red line – which represents modafinil – you’ll notice that after about 1 hour we’re up to plasma concentration of 3 ug/mL.

Two hours later, plasma concentrations peak at 4 ug/mL. So how long does modafinil take to kick in? It takes about 1 hour to get to 75% of the Cmax or the maximum concentration that the drug will attain.