You may have noticed your daily spend on Google Adwords has increased recently. Google has brought in a new rule effecting how your bids are used. The new rule enables them to 'overspend' up to twice your bid as long as it doesn't go over your budget set for the month.
If your campaign rarely meets it's daily spending limit or you use automated bidding this new rule won't effect you, but if you are manually setting your bids and they often reach their daily budget it will.
If you set a daily budget for your campaign of £20 a day, this is effectively a £600 a month budget. So, the new rule means that if you did not meet your budget on some days but did on others that Google assumes you'd like to be spending more on the days you did. This means that it will spend up to £40 on those days. This will be done automatically without checking with you first.
If you have set daily budgets knowing that some days you will underspend, you may be caught out spending more than you planned. Make sure you check your daily budgets are in line with what you plan to spend in a month or risk your account spending going up!