pandas 3 removed frequency aliases 'H', 'T', 'M', 'Q', 'Y', 'A' — use 'h', 'min', 'ME', 'QE', 'YE'
# before
df.resample("M").sum(); pd.date_range("2025", periods=24, freq="H"); s.rolling("5T")
# after
df.resample("ME").sum(); pd.date_range("2025", periods=24, freq="h"); s.rolling("5min")
Period frequencies are separate: pd.Period(..., freq="M") still means month for periods.
Symptom
df.resample("M"), pd.date_range(..., freq="H"), freq="T", freq="A", or pd.Timedelta(1, "H") worked with a FutureWarning on pandas 2.2/2.3 and now raise on pandas 3.0.
Cause
pandas 3.0.0 (2026-01-21) enforced the 2.2-era deprecations:
| Removed | Use |
|---|---|
M (MonthEnd), BM, SM, CBM |
ME, BME, SME, CBME |
Q, BQ (QuarterEnd) |
QE, BQE |
Y, BY, A, A-DEC, BA (YearEnd) |
YE, BYE, YE-DEC |
AS, BAS (YearBegin) |
YS, BYS |
H, BH, CBH (Hour) |
h, bh, cbh |
T, L, U, N (Minute, Milli, Micro, Nano) |
min, ms, us, ns |
Also newly deprecated in 3.0: lowercase d, b, c, w in favour of D, B, C, W.
Verify
grep -rnE "freq=['\"](M|Q|Y|A|H|T)['\"]|resample\(['\"](M|Q|Y|A|H|T)['\"]" src/ is empty and tests pass on pandas 2.3 with -W error::FutureWarning.
Sources
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