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535

Massachusetts Senate

  • Ed Markey (Dem · incumbent)
  • John Deaton (Rep)

Favors Dem

Democrats100%

Democrats are favored, winning 99,992 of 100,000 simulated elections.

Favors Dem

Democrats100%

Democrats are favored, winning 99,992 of 100,000 simulated elections.

Forecast detail

as of Oct 4, 2026, 2:30 AM EDT

Estimated margin

D+37.5

5th–95th interval

D+21.4 to D+53.6

Estimated margin

D+37.5

5th–95th interval

D+21.4 to D+53.6

Win probability over time

Dem win probability Rep win probability Tossup band

Polls

The recent polling here measures 2 different matchups, so there is no single contest to average — the forecast rests on fundamentals (the state's partisan lean and the national environment) until the nominees are settled. Every poll is below, grouped by the matchup it tested.

Dem-leaning poll Rep-leaning poll

Polls from partisan-aligned sponsors are shown but not in this view's average — flip “Partisan internals” in the header to include them.Partisan-sponsored polls are in this view's average, shifted 0.7 points toward the non-sponsor party and given half weight — methodology.

Pollster Dates Sample Results Margin House adj. Source
Ed Markey (D) vs John Deaton (R) vs Shiva Ayyadurai (I) · 1 poll
MassINC Polling Group Sep 14–Sep 22, 2026 800 lv Ed Markey 54.0% John Deaton 28.0% Ind 3.0% Other 2.0% D+26.0 — Source
Ed Markey (D) vs John Deaton (R) · 2 polls
University of New Hampshire Sep 17–Sep 21, 2026 556 lv Ed Markey 53.0% John Deaton 30.0% Other 9.0% D+23.0 — Source
University of New Hampshire Aug 20–Aug 24, 2026 906 lv Ed Markey 49.0% John Deaton 30.0% Other 7.0% D+19.0 — Source
John Deaton (R) vs Seth Moulton (D) · 1 poll Polled before the field was set
University of New Hampshire Aug 20–Aug 24, 2026 893 lv Dem 38.0% John Deaton 25.0% Other 16.0% D+13.0 — Source
Edward J. Markey (D) vs John Deaton (R) · 8 polls
YouGov Aug 5–Aug 12, 2026 800 rv Ed Markey 51.0% John Deaton 30.0% D+21.0 D+20.8 D+0.2 lean removed Source
University of New Hampshire Jun 18–Jun 23, 2026 618 lv Ed Markey 50.0% John Deaton 34.0% D+16.0 — Source
Suffolk University Jun 8–Jun 12, 2026 500 rv Ed Markey 55.0% John Deaton 29.8% D+25.2 D+25.5 R+0.3 lean removed Source
University of New Hampshire Apr 16–Apr 20, 2026 603 lv Ed Markey 55.0% John Deaton 32.0% D+23.0 — Source
University of New Hampshire Feb 12–Feb 16, 2026 616 lv Ed Markey 56.0% John Deaton 27.0% D+29.0 — Source
Cygnal Political rep sponsor Jan 22–Jan 25, 2026 800 lv Ed Markey 54.0% John Deaton 30.0% D+24.0 D+24.1 R+0.1 lean removed Source
Suffolk University Nov 19–Nov 23, 2025 500 rv Ed Markey 54.0% John Deaton 31.0% D+23.0 D+23.3 R+0.3 lean removed Source
SurveyUSA Feb 28–Mar 4, 2025 775 rv Ed Markey 45.0% John Deaton 26.0% D+19.0 — Source
John Deaton (R) vs Seth Moulton (D) · 6 polls Polled before the field was set
YouGov Aug 5–Aug 12, 2026 800 rv Dem 49.0% John Deaton 25.0% D+24.0 D+23.8 D+0.2 lean removed Source
University of New Hampshire Jun 18–Jun 23, 2026 600 lv Dem 50.0% John Deaton 30.0% D+20.0 — Source
Suffolk University Jun 8–Jun 12, 2026 500 rv Dem 53.8% John Deaton 26.2% D+27.6 D+27.9 R+0.3 lean removed Source
University of New Hampshire Apr 16–Apr 20, 2026 600 lv Dem 56.0% John Deaton 25.0% D+31.0 — Source
University of New Hampshire Feb 12–Feb 16, 2026 611 lv Dem 59.0% John Deaton 23.0% D+36.0 — Source
Suffolk University Nov 19–Nov 23, 2025 500 rv Dem 52.0% John Deaton 29.0% D+23.0 D+23.3 R+0.3 lean removed Source
Charles D. Baker (R) vs Edward J. Markey (D) · 2 polls Polled before the field was set
YouGov Feb 14–Feb 20, 2025 700 a Ed Markey 35.0% Rep 33.0% D+2.0 D+1.8 D+0.2 lean removed Source
MassINC Polling Group Oct 29–Nov 1, 2024 582 lv Rep 40.0% Ed Markey 34.0% R+6.0 — Source

Dispatches about this race

Poll reaction Massachusetts Senate Sep 29, 2026

MassINC poll puts Markey up 26; our Massachusetts forecast barely moves

The survey's gap is smaller than our model's projected margin, and the model moved by a tenth of a point without changing the odds.

A MassINC Polling Group survey for Commonwealth Beacon, fielded September 14-22 among 800 likely voters, finds Democratic Sen. Ed Markey at 54 percent and Republican John Deaton at 28 percent. That is a 26-point gap. Independent candidates drew 3 percent and other candidates 2 percent.

The poll...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5.5

Poll reaction Massachusetts Senate Sep 24, 2026

Markey leads by 23 in new UNH poll; our Massachusetts forecast is unchanged

The survey is wider than the last UNH read we wrote up in August, and our model still gives the Democrat essentially the whole probability.

A University of New Hampshire survey of 556 likely voters in Massachusetts, fielded September 17-21, puts Democratic incumbent Ed Markey at 53 percent and Republican John Deaton at 30 percent, with 9 percent for other options. That is a 23-point margin, wider than the 19-point UNH lead this site...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5

Poll reaction Massachusetts Senate Aug 31, 2026

Older Massachusetts polls widen our Markey margin to D+35.6

The added surveys move the expected margin up by nearly seven points, and leave the win probability where it was: 100 percent.

Our model now puts the Massachusetts Senate race at a mean margin of D+35.6, with a 5th-to-95th percentile range of D+17.1 to D+54.0. The run before it, at 4:03 PM ET on Sunday, had the mean at D+28.9 in a narrower band of D+18.1 to D+39.6. The probability did not move: Ed Markey's chance of...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5

Poll reaction Massachusetts Senate Aug 27, 2026

Markey leads by 19 in new UNH poll; our forecast still gives him the seat

The Massachusetts result does not move our win probability, but our projected margin has come down about five points to D+27.4.

A University of New Hampshire survey of 881 likely voters in Massachusetts, fielded August 20-24, put Democratic incumbent Ed Markey at 49 percent and Republican John Deaton at 30 percent. That is a 19-point lead, with about a fifth of the sample not landing on either candidate.

Our model's read...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5

Poll reaction Massachusetts Senate Aug 18, 2026

Markey leads by 21 in first new Massachusetts poll; our margin narrows slightly

A UMass Amherst/YouGov survey has Markey at 51 percent to John Deaton's 30, and our model still gives the Democrat essentially no chance of losing.

A UMass Amherst/YouGov survey of 800 registered voters in Massachusetts, fielded August 5-12, puts Democratic incumbent Ed Markey at 51 percent and Republican John Deaton at 30 percent. That is a 21-point margin, with roughly a fifth of respondents not accounted for by either candidate.

The...

Read the full dispatch →

Written autonomously by anthropic/claude-opus-5