Explaining gaps in your employment history

Suppose you have a substantial gap in your CV when you did not have a job. If you don’t say something about it in your covering letter, the prospective employer might draw their own negative conclusions and discount you as a candidate. Similarly, if you are offered an interview, it’s inevitable that you will be asked about any gaps. You need to practice an adequate response, so that you won’t be caught out when the question comes up.
The best way to explain a gap depends on the situation and what you did with the time. Gaps of less than a couple of months at a time or those that occurred many years ago are not so much of a problem. On your CV, a way to avoid drawing attention to these sorts of gaps is to give only the years for your employment. So, as long as you were in a particular job for over a year, you could say, for example, 2004 - 2008 rather than November, 2004 - April, 2008.
In any case, even longer gaps in employment can obviously have been used constructively:
You may have been raising children. Parents learn valuable skills while bringing up children and running the home, such as time-management and prioritizing, budgeting, managing conflict, and keeping calm under pressure.
These and the many other skills you use in your daily life are called transferable skills, because you will also be able to use them in the workplace when you get a job. They can be gained through responsibilities in the home, to family and friends, voluntary work, DIY projects, maintaining a website or writing a blog, and so on.
You may have been caring for a sick relative which, again, will have equipped you with all sorts of transferable skills.
Whether you’ve been caring for children or relatives, it is a good idea to say how the situation has now changed, that you have made any necessary care arrangements and that you are now able to return to the workplace, armed with these transferable skills.
You may have done some training and gained new skills and qualifications, which will prove to the prospective employer that you’re utilising your time effectively and thinking ahead.
You may also have done or be doing some voluntary work. Remember, voluntary work, if it is (or was) regular and substantial in nature should be included in your Employment History or Work Experience section of your CV, where it will be more noticeable. Treat it as a job like any other.
Many employers believe that time spent travelling can also be beneficial. An awareness of different cultures, customs, and traditions and a familiarity with languages other than English could prove to be an asset, especially to organisations that also do business overseas. Don’t say something like, ‘I spent six months travelling because I couldn’t find a job in this country.’ Instead, say, ‘I took six months out to immerse myself in a different culture and feel that I’ve not only gained a new perspective on the world, but also gained a real sense of self-reliance.’
Of course, some gaps are easier to explain than others. Taking time out for travelling, for example, is less difficult to talk about than a lengthy absence due to illness. Don’t say, ‘I have a recurring health problem which has made it difficult for me to hold down a job’. Instead, say something like, ‘Due to a recurring medical condition I felt unable to continue in my previous position. However, I’ve now returned to full health (or, my health problem is now fully under control) and feel ready to take on my next challenge.’
If you’ve been in prison you could describe any learning opportunities or other activities you got involved in. You could also describe the circumstances leading up to your offence, but keep it brief. Concentrate on explaining how you dealt with these difficult times and learned from them, and that you’ve now definitely moved on and changed for the better.

Help and advice for ex-offenders, including disclosing convictions and presenting your past in a positive light, can be found in NACRO’s guide to Disclosing criminal records and at the National Careers Service website
Whatever the reason for gaps in your CV, your cover letter or email gives you the space to explain what you’ve done with the time and what you’ve learned. Say how organised and determined you are in your approach to job hunting.
Don’t be tempted to extend the length of time you were in a particular job to cover a gap because a prospective employer may request a reference from your previous employer and will find out that you have been dishonest. Lying about a gap will do your chances of employment more harm than explaining them properly. What's important is to tell the truth, be positive and make sure that you come across as enthusiastic and ready for work.