coupon vs voucher difference

In the OED the noun coupon has four principal senses and many sub-senses, but at its most general - sense 1. coupon means:

A separable certificate or ticket, of which a series are attached to, and form part of, certain original or principal certificates, in order that they may be severally detached and given up as required.

Coupons can be used for many purposes - but in essence they are certificates which confirm some sort of (usually)commercial entitlement.

A voucher has a separate range of meanings, the older of which have a strictly legal essence e.g.

sense 1a:

The summoning of a person into court to warrant the title to a property. voucher over

sense 2a:

transf. A piece of evidence; a fact, circumstance, or thing serving to confirm or prove something; a guarantee.

sense 2b:

A written document or note, or other material evidence, serving to attest the correctness of accounts or monetary transactions, to prove the delivery of goods or valuables, etc.

It is when you get to sense 2d, that voucher becomes synonymous with some of the senses of coupon: But note that the earliest example of this rather everyday use is from 1947. sense 2d.

d. A document which can be exchanged for goods or services as token of payment made or promised by the holder or another (see also quot. 1947).

1947 Sun (Baltimore) 12 May 2/5 Stefan has gone through a stack of vouchers—expense accounts—from the American Embassy.

1955 Evening Standard 28 Oct. 15/3 (heading) Doorman/timekeeper for staff and goods entrance... Pension scheme, welfare fund, luncheon vouchers, etc.

1960 S. Unwin Truth about Publisher ii. xix. 353 The New Zealand Company had not given me an actual ticket..but a voucher instructing their agent to issue me a ticket.

It seems clear that before and during WW2, coupon would have been the principle term for a commercial document proving entitlement. The UK's wartime food rationing system was based on coupons. But, from mid-century it would seem that the old legal term voucher gained prominence.

In U.S Retail sales, a coupon is applied after while a discount is applied before.

Say I am a wholesaler and I have several a high volume customer Name GREATCUSTOMER. I give GREATCUSTOMER a better price if they buy case quantities then my normal customers who buys just 1 of an item.

The base price of the item is adjusted for GREATCUSTOMER. That is a Discount

Discounts are applied before any other calculations are done. Such as TAX, VAT, Shipping (if it is based upon price), etc.

A coupon is different, a coupon normally does not adjust the base price of an item. And usually it taken off the total of the sale. (Some U.S. states treat coupons different, some require the coupon amount to be taken before tax is calculated and some states require coupon after tax is calculated (these states tax the base price of the item first, so sales tax is higher) In these later states, often retail stores offer "discounts" instead of regular coupons.

To sum it up, discount is taken before any calculations on an order are done. coupons after.

Usually a voucher can be exchanged for physical goods. Using it as a term for a reciept is an archaic usage of the term and not in common usage today.