Home/PostalMag/Postal TSP/TSP Rates of Return September 2019 Postal TSP TSP Rates of Return September 2019 PostalMag · Thursday, October 03, 2019 Most Thrift Savings Plan funds showed modest gains for the month of September 2019. Only the F Fund had a negative return for the month. YTD, the C, S and I Funds are showing strong gains for the year.