The C Fund, which tracks Standard & Poor's 500 Index of stocks in the largest domestic companies, gained 4.43 percent last month, far outperforming the others. That increase brought the C Fund's 12-month total growth to 15.23 percent.
The international investments represented in the 401(k)-style retirement plan's I Fund had the second-best showing last month, posting gains of 3.76 percent. But the I Fund outperformed the other funds in terms of growth for the year, with 12-month returns of 18.99 percent.
The S Fund, which invests in small- and mid-sized companies by tracking the Dow Jones Wilshire 4500 Index, grew 2.51 percent last month, for a 12-month gain of 11.67 percent.
The fixed-income bonds in the F Fund had minimal gains for April, coming in at 0.53 percent. The fund's 12-month earnings stood at 7.37 percent.
Finally, the government securities (G) fund -- which is the most reliable TSP option, with a guaranteed small but steady growth -- earned 0.42 percent last month for a yearlong 5.03 percent increase.
TSP participants can also invest in five life cycle funds, made up of a mix of the underlying basic funds. The L funds shift participants' investments from riskier to more conservative blends as they age. L funds with riskier allocations posted the strongest gains for April.
L 2040, intended for employees with a target retirement date around the year 2040, gained 3.28 percent. The L 2030 Fund earned 2.95 percent; the L 2020 gained 2.58 percent; the L 2010 increased 1.76 percent; and the L Income, designed for employees with planned retirements in the very near future, grew 1.08 percent.
The L funds with riskier allocations also earned more over 12 months. L 2040 gained 14.27 percent, L 2030 grew 13.11 percent, L 2020 gained 12.04 percent, L 2010 earned 9.63 percent and L Income made 7.30 percent.