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Month Explorer

How each TSP fund has done in each calendar month since 2004, and every way to trade a month with up to 2 switches. Find the ways that worked, chain twelve into a plan and test it, with the years from 2018 kept apart to check it on.

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Each fund, month by month

Each fund's average return in each calendar month, held for the whole month: on 2004 to 2017, the years Best Fit is chosen on, and from 2018, the unseen years through September 2026. Under each average, the years it rose.

  • JanuaryF led 2004–2017; S from 2018
    January: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.25%14 of 14 up+0.25%9 of 9 up
    F Fund+0.70% (led)11 of 14 up+0.31%5 of 9 up
    C Fund−0.85%7 of 14 up+2.19%6 of 9 up
    S Fund−0.10%7 of 14 up+2.55% (led)6 of 9 up
    I Fund−0.86%8 of 14 up+2.41%5 of 9 up
  • FebruaryS led 2004–2017; G from 2018
    February: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.23%14 of 14 up+0.23% (led)9 of 9 up
    F Fund+0.31%11 of 14 up−0.21%3 of 9 up
    C Fund+1.01%10 of 14 up−0.90%3 of 9 up
    S Fund+1.37% (led)10 of 14 up−0.21%5 of 9 up
    I Fund+0.95%9 of 14 up−0.42%5 of 9 up
  • MarchS led 2004–2017; G from 2018
    March: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.25%14 of 14 up+0.26% (led)9 of 9 up
    F Fund+0.12%7 of 14 up−0.04%5 of 9 up
    C Fund+1.92%10 of 14 up−0.96%5 of 9 up
    S Fund+2.56% (led)10 of 14 up−3.70%3 of 9 up
    I Fund+1.70%10 of 14 up−1.64%5 of 9 up
  • AprilI led 2004–2017; C from 2018
    April: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.25%14 of 14 up+0.25%9 of 9 up
    F Fund+0.41%10 of 14 up−0.36%6 of 9 up
    C Fund+1.85%11 of 14 up+2.35% (led)6 of 9 up
    S Fund+1.58%9 of 14 up+1.55%5 of 9 up
    I Fund+2.78% (led)10 of 14 up+2.34%7 of 9 up
  • MayS led 2004–2017, and again from 2018
    May: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.26%14 of 14 up+0.26%9 of 9 up
    F Fund+0.21%8 of 14 up+0.52%7 of 9 up
    C Fund+0.44%10 of 14 up+1.87%7 of 9 up
    S Fund+0.56% (led)9 of 14 up+2.00% (led)6 of 9 up
    I Fund−0.73%7 of 14 up+1.47%6 of 9 up
  • JuneG led 2004–2017; S from 2018
    June: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.25% (led)14 of 14 up+0.26%9 of 9 up
    F Fund+0.15%8 of 14 up+0.33%6 of 9 up
    C Fund−0.78%8 of 14 up+2.19%7 of 9 up
    S Fund−0.21%7 of 14 up+2.79% (led)7 of 9 up
    I Fund−0.59%5 of 14 up+0.57%4 of 9 up
  • JulyI led 2004–2017; C from 2018
    July: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.27%14 of 14 up+0.26%9 of 9 up
    F Fund+0.69%11 of 14 up+0.68%6 of 9 up
    C Fund+1.62%9 of 14 up+3.22% (led)8 of 9 up
    S Fund+0.91%6 of 14 up+3.18%7 of 9 up
    I Fund+1.93% (led)9 of 14 up+1.30%6 of 9 up
  • AugustF led 2004–2017; C from 2018
    August: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.25%14 of 14 up+0.26%9 of 9 up
    F Fund+0.86% (led)11 of 14 up+0.21%5 of 9 up
    C Fund−0.27%9 of 14 up+1.49% (led)6 of 9 up
    S Fund−0.34%7 of 14 up+1.11%6 of 9 up
    I Fund−0.76%6 of 14 up+0.44%5 of 9 up
  • SeptemberC led 2004–2017; G from 2018
    September: average month return of each fund held all month
    Fund2004–20172018–2026
    G Fund+0.24%14 of 14 up+0.25% (led)9 of 9 up
    F Fund+0.17%9 of 14 up−1.01%2 of 9 up
    C Fund+0.64% (led)10 of 14 up−1.62%4 of 9 up
    S Fund+0.61%10 of 14 up−2.54%3 of 9 up
    I Fund+0.52%10 of 14 up−1.43%4 of 9 up
  • OctoberC led 2004–2017, and again from 2018
    October: average month return of each fund held all month
    Fund2004–20172018–2025
    G Fund+0.25%14 of 14 up+0.25%8 of 8 up
    F Fund+0.12%11 of 14 up−0.71%2 of 8 up
    C Fund+1.06% (led)9 of 14 up+0.89% (led)4 of 8 up
    S Fund+0.59%9 of 14 up+0.24%6 of 8 up
    I Fund+0.69%9 of 14 up−0.77%4 of 8 up
  • NovemberS led 2004–2017, and again from 2018
    November: average month return of each fund held all month
    Fund2004–20172018–2025
    G Fund+0.23%14 of 14 up+0.26%8 of 8 up
    F Fund+0.31%8 of 14 up+1.48%7 of 8 up
    C Fund+1.25%11 of 14 up+4.59%7 of 8 up
    S Fund+1.62% (led)11 of 14 up+5.75% (led)6 of 8 up
    I Fund−0.08%8 of 14 up+4.32%5 of 8 up
  • DecemberI led 2004–2017, and again from 2018
    December: average month return of each fund held all month
    Fund2004–20172018–2025
    G Fund+0.25%14 of 14 up+0.25%8 of 8 up
    F Fund+0.26%8 of 14 up+0.34%3 of 8 up
    C Fund+1.40%11 of 14 up−0.16%5 of 8 up
    S Fund+1.99%11 of 14 up−0.55%4 of 8 up
    I Fund+2.11% (led)10 of 14 up+1.49% (led)5 of 8 up

The fund that led a month on 2004 to 2017 led it again from 2018 in 4 of 12 months.

Best Fit: the best plan in hindsight

Of every plan that trades each month one of these ways, this one grew the most on 2004 to 2017: 37.1% a year, against 8.7% for the C Fund. It was chosen knowing how those years turned out. On the years since, which it was not chosen on, it made 15.7% a year against 14.5%.

2004–2017, chosen on
37.1%
C Fund 8.7%
From 2018, unseen
15.7%
C Fund 14.5%

It moves 24 times a year. A plan picked with hindsight tends to look better than it will do; the blind test below is the fair check.

Its twelve months
  1. January, starting in I: Into the F Fund on the 1st trading day, then the S Fund on the 12th trading day.
  2. February, starting in S: Into the F Fund on the 12th trading day, then back to the S Fund on the last trading day.
  3. March, starting in S: Into the G Fund on the 3rd trading day, then back to the S Fund on the 6th trading day.
  4. April, starting in S: Into the F Fund on the 2nd trading day, then the I Fund on the 5th trading day.
  5. May, starting in I: Into the F Fund on the 2nd trading day, then the S Fund on the 14th trading day.
  6. June, starting in S: Into the G Fund on the 2nd trading day, then back to the S Fund 3 trading days before month end.
  7. July, starting in S: Into the F Fund on the 1st trading day, then the I Fund 3 trading days after Independence Day.
  8. August, starting in I: Into the F Fund on the 1st trading day, then the S Fund on the 17th trading day.
  9. September, starting in S: Into the I Fund on the 11th trading day, then the G Fund on the 14th trading day.
  10. October, starting in G: Into the I Fund on the 8th trading day, then the C Fund on the 9th trading day.
  11. November, starting in C: Into the G Fund on the 6th trading day, then the S Fund on the 13th trading day.
  12. December, starting in S: Into the G Fund on the 6th trading day, then the I Fund on the 11th trading day.
Open Best Fit in the builderOpen it in the backtester

Build your own plan

See all 347,140 ways to trade a month with their numbers, filter and sort them, pick one for each month, pin the ones you want kept and let Best Fit fill the rest. The plan's results come from the backtester, and the link carries the plan.

Best Fit, blind tested

Best Fit is found with hindsight. This test takes the hindsight out: for each year from 2018, Best Fit is found on 2004 to the year before, with every way allowed, then followed for that one year and set beside the C Fund.

$10,000 moved into each year's pick, 2018 to 2025, would be about

$29,900

Left in the C Fund the whole time: about $29,100.

Growth per year
14.7%
C Fund 14.3%
Beat the C Fund
4 of 8
full calendar years
Promised
34.2%
the picks' average record before they were picked
Delivered
15.2%
their average in the year they were picked for
Each year's Best Fit
YearRecord beforeThat yearC Fund
201837.1%3.6%−4.4%
201934.7%23.2%31.5%
202034.5%11.1%18.3%
202135.1%19.0%28.7%
202234.3%−2.5%−18.1%
202332.7%32.2%26.2%
202433.3%9.7%25.0%
202532.3%25.3%17.8%
2026*32.2%9.1%13.8%

Record before: that year's Best Fit's growth per year on 2004 to the year before, the years it was found on. That year and C Fund: the calendar-year return. Each year opens its plan in the backtester. * 2026 so far, through Oct 27, 2026; not counted in the totals.

The library's blind test asks the same question of the strategy library's plans.

Official TSP share prices through Oct 27, 2026.

Past performance does not predict future returns. This is not investment advice.

How it works

  • A way to trade a month starts in the fund the plan holds when the month begins and makes up to 2 switches, each moving the whole balance into the G, F, C, S or I Fund. The TSP allows two moves a month, then moves into the G Fund only, so any way can be followed in any month.
  • Switches fall on days the backtester offers that land inside the month every year: the 1st to 20th trading day, the last trading day and the three before it, and up to three trading days either side of a holiday in the month.
  • Each month is measured in every year from 2004 in which it is complete, this year's complete months included. 2004 to 2017 are the fitted years: Best Fit and the honest order's shortlist are chosen on them. The years from 2018 are unseen, kept to check those choices.
  • A way's return follows the backtester exactly, each switch made at the close of its day, and a plan's results come from the backtester itself.
  • The ways, their numbers and Best Fit are worked out in your browser from the official share price file.

The methodology says more, and how to read a backtest explains why a plan's past and its future so often disagree.