Word Choice – Do You Need ‘On’ or ‘Upon’ When Referring to Dates?

prepositionsword-choice

When defining a date, should I use on, upon or when, or can I leave these words out?

For example, can I say:

The date the company allots the securities is known as the Despatch Date.

or should I say:

The date on which/upon which/when the company allots the securities is known as the Despatch Date.

Best Answer

According to 1913 Webster's upon is interchangeable with on, however if you look at ngrams

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you will find that upon is used less and less as there is, I believe, a slight archaic and/or formal tone to it.

All your sentences seem correct to me, but I would choose shorter and simpler constructs (using only when or without conjunction).

Here is ngrams graph that compares upon which and on which

enter image description here

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