Do you need to tell your employer you are retiring?
Whether or not you need to tell your employer you are retiring might seem like a silly question, but the answer is surprisingly it depends. It depends mostly on how your pension is structured. If your pension is tied to your company, then yes they will need to be warned that you are retiring. If they have nothing to do with your pension and it's completely separate. Then you don't need to tell them anything except that you are leaving. Again, it's important to check. How your pension is structured will play a big part. Plus, it's a good idea to tell your employer anyway. That way you don't need to give a detailed reason for leaving and you don't leave them shorthanded.
How much warning should your employer be given?
It is normally considered polite to give a month's notice when you are leaving your job. Regardless of if you are retiring or not. Most companies ask for about 2 weeks' notice, sometimes 3. If you are required to give this much notice when you quit you will also be required to give that much notice when you retire. If you don't give notice and just stop turning up, well, you may find that you lose out on some of the money they owed you. Your pension probably won't be in jeopardy, but why risk it for an extra few weeks of retirement? You are about to have nothing but time. If you have a good relationship with your employer, giving them lots of time would be my recommendation. The more warning, the easier they will find replacing you.
What are the legal obligations for informing your employer?
You are likely not legally required to inform your employer at all. Most of it is to do with your contract and your moral obligations. You are very unlikely to be sued for leaving early. It is not worth it from their perspective to even hire a lawyer. That being said, your pension may require you to give warning, and if that's the case you must ensure you do so. Or, you may have your pension withheld. This is not so much a legal issue but a technical one. When you inevitably have to sue to get your full pension released to you, then it becomes a legal issue.
What are the advantages of giving lots of warning?
Just because you are retiring doesn't mean you plan on staying retired. You may decide you wish to go back to work if that's the case giving your employer lots of notice will keep you in good stead should you wish to return. It also gives your employer time to find someone to replace you. If you give them enough warning, it may even give you time to train the replacement. This is not an obligation at all. But, if you like the place you work and respect your employer and your colleagues this is a good idea. You will be glad you ended things on a good note.
What are the advantages of giving the bare minimum warning?
Just as it is a nice idea to give lots of warnings for the benefit of your employer, it can be very beneficial to give little to no warning for yourself. A shady employer may use the news as an excuse to try and fire you and have your pension voided. This won't work, of course, but the threat can be enough to make you doubt yourself. By giving them minimal warning, you can be gone before they have time to do much about it. It can also save you a lot of headaches. Telling your employer you are retiring in 2 weeks is a clear agreement. Telling them, you'll retire in 3 months means they might try and strong-arm you into staying "just a little longer." Lastly, the sooner you can leave the workforce for good, the better. You've worked hard; you've put in your fair share of hard days. It's time to hang up your hat. There is no use prolonging it.
What are some red flags to look for from your employer?
If your employer starts getting agitated that you are retiring and starts making threats, walk away and tell them you'll be contacting your lawyer. This alone is enough for most people to roll over. Some less obvious issues are employers who try to guilt-trip you. Insisting they just need you for another year, they can't finish this project without you, how are they supposed to find a replacement soon enough, leave. Just walk away. They'll do their best to keep you forever if they can. You don't owe anyone any more than you have already given. You've earnt your retirement, it is not theirs to take away.
Hopefully, you now have a better idea of what to expect when handing in your notice. Remember, how much you are required to give will be stated in your contract. If it is never explicitly stated, then work off of leaving the company not specifically retiring. If you aim to give 2 weeks notice, you are normally good to go. Most places don't expect anything more than that, some are grateful to get any notice at all!