What Were They?
The first plague to befall Egypt was the Nile River and all its streams turning to blood (Exodus 7:15 - 25). The second was a plague of frogs (8:1 - 15), the third of lice (8:16 - 19), the fourth of flies (8:20 - 32), and the fifth was a disease that killed the majority of Egypt's cattle (9:1 - 7).
The sixth plague brought boils upon man and beast (Exodus 9:8 - 12). The seventh one to strike Egypt was a grievous hail that destroyed both the flax and barley (9:13 - 35).
The eighth calamity was a devasting swarm of locusts (Exodus 10:1 - 20) while the ninth was three days of complete darkness over the land (10:21 - 29). The tenth, and final, calamity to befall Egypt was the death of the firstborn of both man and beast (11:1 - 12:36).
What Does Usher Say?
Usher's famous chronology states that all ten of Egypt's plagues occurred within a span of twenty-seven days, between April 9 and May 5 (Adam Clarke's Commentary). Such a short span lacks Biblical evidence, however, as another commentary noted.
"There is a common notion that the ten plagues followed each other with breathless speed, and were completed within a few weeks. But nothing in the narrative asserts or even hints this, and what we do know is in the opposite direction." (Expositor's Bible Commentary).
Usher's May 5 Passover date is, if for no other reason, simply incorrect as this spring Holy Day has never fallen in May! Please see our research on Holy Day dates throughout history for more information.
What Do We Know?
The Bible does not give us any evidence regarding when eight of Egypt's ten plagues took place. There are clues, however, for when the seventh and the tenth one occurred.
Let's start with the easiest plague date to determine. Egypt's tenth and final judgment occurred at midnight Nisan 14 (see Exodus 12). This corresponds, based on an Exodus year of 1445 B.C., to the start of Monday April 11.
Egypt's seventh plague was an unprecedented rain of hail coupled with thunder and even fire (Exodus 9:13 - 35)! One of the devastating consequences of the hail was that the nation's barley and flax was destroyed.
And the flax and the barley were stricken, for the barley was in the head, and the flax was in bud. But the wheat and the rye (spelt) were not stricken, for they had not grown up (Exodus 9:31 - 32).
Flax and barley in Egypt blossoms between late January and early February. It is therefore highly likely the seventh plague took place sometime in early February.
Putting It All Together
The time between early February and April 11 is roughly about eight weeks. This information can help us approximate the total duration of Egypt's plagues.
". . . and all that is tolerably sure is, that the seventh plague occurred in February, and there were eight weeks therefore, or about two months, between the seventh and tenth plagues; so that between each of the last three there would be an interval of fourteen or twenty days.
"And if we suppose that there was a similar interval in the case of all the others, the first plague would take place in September or October - that is to say, after the yearly overflow of the Nile, which lasts from June to September." (Keil and Delitzsch Commentary on the Old Testament).
If the first plague began in late September, with the last taking place on April 11, we end up with Egypt suffering from God's wrath for a period lasting about six and one-half months long.