Most couples leave this later than they should. The short version: three to four months before the date gives you room for sizing, plus a buffer for the odd supplier delay. If you want a ring made to your own design, stretch that to five or six months. Booking early costs nothing and removes the one variable no bride or groom wants near the wedding, which is a ring that isn't ready.
So why isn't there a single number? Because the answer depends on what you're buying. A plain band pulled from a jeweller's existing stock can be sized and ready inside a fortnight. A piece made for you, set with stones picked by hand, runs on a slower and more interesting clock.
The custom ring question
Couples drawn to something one-of-a-kind tend to underestimate the calendar. A design consultation, the CAD drafts that follow, casting, stone setting and the final polish each add their own days or weeks. A bespoke studio like Harry & Co will often quote six to eight weeks of production once a design is signed off, and the design conversation before that can run another two or three weeks as you refine the metal and the setting.
That wait buys you something a display cabinet can't: a band that matches how you live and what you pictured when you first started looking. If bespoke appeals to you, book the first consultation soon after you've set a date. The studios worth visiting tend to keep a waitlist, and the good ones won't rush the part that matters.

Sizing is rarely a same-day fix
Finger size moves around more than people expect. Warmth, cold, exercise and even the time of day all nudge the number up or down. A reputable jeweller will measure you on more than one occasion before committing to a final size, and that alone can add a week or two to the process.
Resizing after the fact is possible with most plain bands, though it takes time you may not have in the final fortnight. Rings with stones set all the way around, known as eternity bands, are far harder to resize and sometimes can't be altered at all. If that's the style you love, accurate measurement up front becomes non-negotiable.
Metal and stone choices change the timeline
A platinum band behaves differently from a gold one at the workbench, and that affects how long a jeweller needs. Platinum is denser and slower to work, so a platinum ring with any detail will sit in production longer than a comparable gold piece. It's a small thing to ask about, but knowing it early saves a nasty surprise later.
Coloured gemstones add another layer. A jeweller sourcing a particular sapphire or a specific cut of morganite may be waiting on stones arriving from a supplier before any work begins. Lab-grown diamonds tend to be quicker to source than rarer mined stones, which can shave a week or more off the front of the schedule if speed is your priority. None of this should put you off the ring you want. It only means the more particular your taste, the earlier you start.
If you've left it late, you still have options
Say the wedding is six weeks out and you've nothing on your finger yet. You're not stuck. Many studios keep a ready-to-wear collection of finished bands that need only sizing, which sidesteps the long production wait. Asking specifically whether a jeweller holds finished stock in your metal and size is the quickest route when the clock is against you.
If your heart is set on bespoke and the date is close, be honest with the jeweller at the first meeting. Some will fast-track a simpler design for a firm deadline. What they can't do is bend physics, so the more flexible you stay on detail, the better your odds of walking down the aisle with the ring on.
A working timeline you can trust
For a plain or lightly detailed band, eight to ten weeks before the wedding is comfortable. For anything custom, give yourself four to six months between the first consultation and collection day, and treat the design stage as part of that rather than an extra on top.
The couples who enjoy this part are the ones who start while the date still feels far away. Ring shopping done early is a pleasant afternoon. Ring shopping done late is a source of stress you can dodge by picking up the phone a few weeks sooner than feels necessary.