How often should I audit my marketing and update the plan?

It depends on the plan period

and you will evaluat and audit it dependin also on the indicators you have made in you plan.

so you can do it frequently every quarter, half year, and annually.

its depend on businesses nature... i will suggest you should change your marketing plan in month or bimonth.

 As Google is updating the algorithm very frequently so it is very important now a days to check the website with every update and so with your search engine preferences. Rest it is always wise to be proactive and do marketing research and analysis weekly or bi-weekly and according to that change the marketing plan as well.

Every Marketing Plan in a Retail Industry has to be evaluated on a daily basis and corrective actions are to be taken.

It depends preferbly once in 06 months

A regular marketing audit - weekly or bi-weekly will give enough for marketers to change or update their plan. In times like this when market dynamics are changing at rapid rate and also their competitors waiting for a mistake from your end to pounce and grab hold of your customer, there is no space complacency.

The second point is most of the market in today's times happen on digital space which can be easily measured unlike the traditional media. So, yes , auditing on a regular basis about the trends and updating plans accordingly gives a good chance to stand out in a competitive environment

There should be a time set for changing the plan for example every 6 months or maybe a year except for urgent cases that you should change it immediatly or maybe wait a longer as the sales are on the increase.

It is all about the strategy of your company. In a plan of a stratgey there should be mentioned how often the audit should take place , and it is better to have at least once and optimally twi audits within an strategy run ( if the strategy has been set for one year) . The very first audit is to check if the plan is right and find the deviations, to take the needful action and amend the plans. The second one is to see if your pruning was okay, if the plan has reached to what you have set, how far or close you are from/to the set goals, ...

It depends on the marketing plan period, quarterly or company policy basis .

sometimes companies perform a complete audit every year some every few years . it also depends on the complexity of the givin industry, the amount of growth now days social media changed the whole root.

It depends on the time period of the plan and the results you are getting.

Generally, you are reporting on sales monthly or quarterly.  If your tactics align with a monthly or quarterly spending pattern this is a good cadence for auditing the plan.

The structure of the plan should serve as the framework to diagnosis the success and weakness of performance.  For example, if sales performed relatively well last month you should try to understand which elements of the plan drove those.  However, the impetus to change the plan will be small.  If sales were lower than expected, you need to examine everything in the plan.