for dates in query need equivalent to sql server syntax

In the query below,
on the where statement. is there a method the same as  "datediff"
WHERE ((DateDiff('d',[date_proposal_completed],Date())<+30) AND ((dbo_temp_proposal_survey_results.wl_status) Is Null));
I need to change this syntax to sql server syntax. Please.

SELECT dbo_temp_proposal_survey_results.proposal_id, dbo_temp_proposal_survey_results.specialist_responsible, dbo_temp_proposal_survey_results.customer_name, dbo_temp_proposal_survey_results.date_proposal_completed, dbo_temp_proposal_survey_results.seller_racf_id, dbo_temp_proposal_survey_results.seller_email, dbo_temp_proposal_survey_results.wl_emailed_on, dbo_temp_proposal_survey_results.wl_survey_completed_on, dbo_temp_proposal_survey_results.wl_status, dbo_temp_proposal_survey_results.wl_Q1_answer, dbo_temp_proposal_survey_results.wl_Q2_answer, dbo_temp_proposal_survey_results.wl_Q3_answer, dbo_temp_proposal_survey_results.wl_Feedback, dbo_temp_proposal_survey_results.wl_ReasonLoss
FROM dbo_temp_proposal_survey_results
WHERE ((DateDiff('d',[date_proposal_completed],Date())<+30) AND ((dbo_temp_proposal_survey_results.wl_status) Is Null));

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Thanks
fordraiders