
The daily budget directly controls the day to day running of the advertiser's entire pay per click (PPC) campaign and it is the primary way to control overall spending. The daily budget protects you from spending your entire monthly budget in a day. Most pay per click services do not have maximum and minimum limits for your daily budget (although some do have a minimum on keyword bids which should not be confused with the daily budget).
The delivery of your pay per click ad (i.e. ad delivery) is directly tied to your daily budget. If it is set too low, pay per click ads may run intermittently throughout the day and will be shut off once the budget is reached. The #1 reason why some advertisers can not find their pay per click ads is they have set their daily budget too low. For advertisers using Google AdWords, they should consider the daily budget that Google recommends. Sometimes Google's recommendation can be very high, but it should be used as a guide when setting your daily budget.
For those pay per click advertisers who have a monthly budget and want to set their daily budget in that regard, most PPC services translate daily budget to monthly by using a 30-day month. For example, if you can only spend $90 a month, divide it by 30 to get a $3 daily budget. Do not divide by 31 or 28. It should also be noted that some pay per click services require the advertiser to set their budget on a monthly basis instead of daily, although most use the daily budget format.