I'll defer to others regarding the literacy rate in Europe but can speak to the American colonies. Pinning down exactly what we mean by "literacy" is complicated and has changed over time. The definition wouldn't be standardized until the late 1800's and the rise of literacy tests for voters. Some government officials in the colonies counted every person who could sign their name. Others asked for self-reporting data (if the person considered themselves literate because they could recite religious passages and sign their name, they'd say yes. As would the tutor who taught Latin at Harvard.) which meant there are discrepancies even in primary sources. You'll often see claims that the American colonies were among the most literate in the world, with rates as high as 95%. This, to a certain extent is true. The number, though, requires some unpacking.

Many of the earlier colonists had a religious motivation for traveling to North America. Several of those religious groups, not all to be sure, saw education as essential to leading a good and spiritual life. Being able to read wasn't necessarily about being educated, it was about keeping Satan at bay. This means there were often uneven rates between the ability to read and the ability to write. While some societies in the colonies advocated literacy for all children, most notably Quakers, others focused only on sons. Meanwhile, those high literacy rates often focus only colonists.

Few white dominated societies attended purposefully to the literacy level of Black or enslaved people so they were rarely considered in the denominator. Additionally, reports of 95% literacy ignore the Indigenous people living in the colonies before, during, and after Europeans arrived. In effect, if you only count 100 white, land-owned white men and 95 of them report they can read contracts and scripture, you get a literacy rate of 95%. If they'd actually counted every person living on North American soil, the percentage would be dramatically lower.

There's a connection between the literacy rate and understanding percentages, to be sure. Those on American soil who experienced formal education (with a tutor or in a school like Boston Latin or Harvard), mathematics was essential to the curriculum. From a study of the history of teaching Mathematics in America^1:

Other topics, also part of the standard abbaco curriculum, were also found in North American cyphering books throughout the 18th century and up to about 1860. Almost all colonial cyphering books that focused on elementary arithmetic included entries on compound operations, currency exchange, reduction, vulgar and decimal fractions, and percentage.

Early colonial newspapers spoke of percentages (often written as per cent, per Cent, or per-cent) to describe taxes, daily interest, and crop yields. The notion of percents and decimals were common in Europe in the 1600's^2, so it's reasonable to assume the educated men who came over would be familiar. Those men would use the concept with their wives who were often partners on the family farm or at their business or trade. Children were also instrumental in helping their parents so they would pick up the concept, even if they didn't experience formal education. Likewise, the enslaved and freed people who worked for/with them so it's safe to assume that the concept was widespread.

Finally, this response by u/Bodombeachbod provides a different look at literacy through the lense of wealthy white women in the colonies.

---

1. Ellerton, N., & Clements, M. K. (2012). Rewriting the history of school mathematics in North America 1607-1861: The central role of cyphering books. Springer Science & Business Media.

2. Whitrow, G. J. (1988). Why did mathematics begin to take off in the sixteenth century? In C. Hay (Ed.), Mathematics from manuscript to print 1300–1600 (pp. 264–269). Oxford, UK: Clarendon Press.