The Bureau of Internal Revenue (BIR) just recently announced the availability of Withholding Tax Calculator for use by all Compensation Earners to enable them to check the computation of the Withholding Taxes deducted from their salaries by their employers.
Just click http://www.bir.gov.ph/index.php/withholding-tax-calculator.html to access the system or visit BIR website: http://www.bir.gov.ph/ found under the quick links of the website.
Please refer http://www.bir.gov.ph/images/bir_files/internal_communications_1/Advisory/Announcement-Withholding%20Tax%20Calculator.pdf of the full text of the BIR announcement.