You asked

When should I tell my boss I’m pregnant?

Most women prefer to keep their pregnancy under wraps for the first twelve weeks or will even wait until they are showing. This is because they are more confident of their pregnancy and the risk of miscarriage goes down significantly. 
Before you make a decision about when to tell your boss, think about a few things:
  • How are you feeling and are you suffering from morning sickness? It’s often easier to ring in for a few hours time off whilst you are feeling unwell if your boss knows that you are expecting instead of thinking that you are just bunking off work.
  • Being aware of the culture of the organisation is important factor too – this will often impact on the timing to deliver your own news especially if they have taken such news in a positive (or negative) manner in the past.   If you are happy that your boss will take your news well, it makes complete sense to tell them sooner rather than later. If you are concerned how they will react, it wouldn’t be unusual to wait to tell them until half way through your pregnancy which also allows you illustrate that your pregnancy hasn’t impacted on work.
  • Before you sit down with your boss, get your thoughts together. Know when you want to finish up (all things being equal). Be aware of what the company’s policy is for maternity leave versus what statutory law requires of your boss. If you are working for a larger company, pregnancy and maternity leave may be formally covered in the HR handbook.
If your company is smaller, it’s more likely that there won’t be a HR department or a handbook in which case asking colleagues is probably the best unofficial advice you can get. In the UK, some larger companies pay full salary during maternity leave, some top up social welfare maternity benefit and others contribute nothing at all in which case you are living on your state paid maternity benefit. Being aware of what the company’s policy is before you sit down with your boss will inevitably be helpful.
In fairness to your boss it’s also helpful to have considered what time off you are thinking about. Are you thinking about taking your full 26 weeks or taking your maternity leave plus parental leave too.   Parental leave is normally unpaid, so consider how long you can afford to go without your salary before committing to anything.

Most bosses will want to know if you are planning on coming back to work and if you already decided to never return, then the fair thing would be to tell your boss of your plans.   Then again, if you haven’t totally decided, leave the door open. 
It is against the law for your employer to mis-treat you during your pregnancy – you cannot be fired or demoted after letting your employer know about your pregnancy. If your company doesn’t have a big HR function that you can take any concerns to, be aware that the law is on your side. The Maternity Protection (Amendment) Act 2004 made significant improvements to the Maternity Protection Act 1994 and now covers matters such as maternity leave, the right to return to work after such leave and health/safety during and immediately after the pregnancy.  The Parental Leave (Amendment) Act 2006 which provides for a period of unpaid parental leave for parents to care for their children and for a limited right to paid leave in circumstances of serious family illness known as force majeure. 
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