bank account in foreign account after retirement

how will opening a bank account in a different country to start saving for when retirement comes and i move to that country will affect my taxes currently. I believe that as long as the account does not exceed 10k anytime during the year, i don;t have to disclose it or the IRA or fill out the FBAR form but what would happen in term to taxes if the account exceeds the 10K during the year and then I file the FBAR report, what gets taxed, the balance on the accounts or the proceeds from the deposits which are made after tax (coming from my salary)?