The notion that a ring should cost some fixed number of months of salary was composed by a diamond marketing department in the middle of the last century, and it has outlived its authors the way good slogans do. It was never guidance. It was a quota with a wedding attached.
What the spending actually looks like
Real budgets scatter across an enormous range, and the middle of that range sits far below what jewelry advertising implies. Four figures buys a genuinely beautiful ring in the current market, particularly since grown stones rewrote the price lists. Five figures buys magnificence, and also buys regret in every case where it was borrowed at card interest.
No one who loves you is auditing the receipt. Anyone auditing the receipt has disclosed something useful before the wedding.
Building the number from the correct end
Start from your own balance sheet, not from a formula. The right figure is one you can pay in cash, or retire within a couple of months, without touching emergency savings or arriving at the engagement carrying a grudge. Then spend that figure in the order that beauty actually follows: cut first, the visible thresholds of color and clarity next, size after that, setting last.
Making a modest number go further
The levers are all elsewhere in this issue: shy carat weights, fancy shapes priced below rounds, halos that flatter, grown stones that halve the bill, and a sapphire or moissanite when the two of you are gleefully untraditional. A smaller budget spent in the right order beats a large one spent alphabetically.
The short of it: set the number from your finances, pay cash or close to it, and spend it in the order cut, thresholds, size, setting.