How to Read Election Results: Margins, Swing and Calls

Election results are read with four numbers: each candidate's vote share, the margin between the top two in percentage points, the swing of that margin since the last comparable election, and how much of the expected vote has been counted. In the 2024 Pennsylvania Senate race, Republican Dave McCormick received 48.8% and Democrat Bob Casey 48.6%, a margin of 0.2 points (R+0.2), or 15,115 votes out of 6,963,137 ^[1]. Results reported on election night are unofficial; a race is called by news organizations when the trailing candidate can no longer catch up, and it becomes official only when election officials certify it weeks later ^[13]^[15].

What is the difference between vote share and margin?

Vote share is the percentage of all votes cast in a race that a candidate received. The margin is the difference between the two leading candidates' shares, in percentage points. DataPorium writes margins as the Republican share minus the Democratic share: "R+3.2" means the Republican led by 3.2 points, and "D+3.2" means the Democrat led by 3.2 points ^[7].

A margin in points is not the same as a percentage change. In Wisconsin's 2024 Senate race, Democrat Tammy Baldwin received 49.3% and Republican Eric Hovde 48.5%, so the margin was D+0.8, or 28,781 votes out of 3,390,787 ^[2]. Shares of minor candidates explain why the top two do not add up to 100%.

Three 2024 Senate races were decided by less than 1 point:

Race	Winner's share	Runner-up's share	Margin	Votes between them
Pennsylvania Senate	48.8% (McCormick, R)	48.6% (Casey, D)	R+0.2	15,115
Michigan Senate	48.6% (Slotkin, D)	48.3% (Rogers, R)	D+0.3	19,006
Wisconsin Senate	49.3% (Baldwin, D)	48.5% (Hovde, R)	D+0.8	28,781

Source: DataPorium Election Results, certified 2024 results ^[1]^[2]^[3].

What is swing, and how is it measured?

Swing is the change in the margin between two elections for the same office in the same place. A positive swing means the margin moved toward Republicans; a negative swing means it moved toward Democrats. Swing describes movement, so a party can gain ground and still lose.

National: the presidential margin moved from D+4.5 in 2020 to R+1.5 in 2024, a swing of 5.9 points toward Republicans ^[4].
Toward Republicans: Hidalgo County, Texas, moved from D+17.1 in 2020 to R+2.9 in 2024, a 19.9-point swing that changed the county's winner. A change of winning party is called a flip ^[5].
Toward Democrats: Larimer County, Colorado, moved from D+15.4 in 2020 to D+17.6 in 2024, a 2.2-point swing toward Democrats in the same year the national margin moved the other way ^[6].

Swing compares like with like. A Senate result is compared with the previous election for the same seat, usually six years earlier, not with the presidential race ^[1].

How is turnout measured?

DataPorium measures turnout as votes cast for the top office on the ballot divided by the citizen voting-age population (CVAP): adult US citizens living in the area, whether or not they are registered ^[7]. In 2024, Minnesota had the highest turnout at 77.2% (3,253,920 presidential votes out of 4,217,845 eligible adults), and Hawaii the lowest at 49.2% ^[7]. Turnout counted against registered voters is higher, because not every eligible adult registers.

Why do vote counts shift after polls close?

The order in which ballots are counted varies by state, so early leads can change. Forty-four states and Washington, D.C., let officials begin processing mail ballots before Election Day, while six states (Alabama, Mississippi, New Hampshire, Pennsylvania, West Virginia and Wisconsin) start on Election Day ^[8]. Pennsylvania cannot begin until 7 a.m. on Election Day, and Wisconsin only after the polls open. Michigan jurisdictions of at least 5,000 people may begin eight days before Election Day, and California may begin as soon as ballots are mailed ^[8].

Results often differ by vote method, which is why the order of counting matters. In the 2024 presidential results that DataPorium can split by vote method (27.9% of all votes), mail ballots went D+23.7 and Election Day ballots went R+20.6 ^[4]. Where mail ballots are reported first, early returns can lean Democratic and then shift toward Republicans; where Election Day ballots are reported first, the shift can run the other way.

Some ballots also arrive after Election Day. Thirty-five states require mailed ballots to be received by Election Day, while 15 states and Washington, D.C., count ballots postmarked by Election Day that arrive later ^[9]. California accepts them up to seven days after Election Day, and Illinois up to 14 days ^[9]. On June 29, 2026, the Supreme Court held in Watson v. Republican National Committee that federal election-day laws do not prevent Mississippi from counting ballots postmarked by Election Day and received up to five days later ^[10].

Pennsylvania's 2024 Senate race shows how much counts move. In unofficial returns on November 13, 2024, McCormick led by 29,338 votes; in the certified result, his lead was 15,115 votes ^[1]^[11].

Expected vote versus precincts reporting

The Associated Press reports an estimate of the share of the expected vote counted, based on past turnout and early-vote data, and refines it as returns arrive. It notes that "precincts reporting" can mislead, because early votes may be reported as a single precinct and a precinct may report only part of its ballots ^[14].

How are races called, certified and recounted?

News organizations, not governments, call races on election night. The AP's Decision Team calls a race only when it concludes that the trailing candidates have no path to victory, and it says it does not make projections ^[13]. Even with almost all ballots counted, the AP may decline to call a race when the margin is generally less than 0.5 points ^[13]. In 2020, the AP declared the presidential winner four days after Election Day; in 2024, it did so at 5:34 a.m. Eastern Time the morning after ^[13].

Results become official through the canvass and certification, under deadlines set by each state ^[15].

State	County deadline	State certification
Florida	Noon on the 13th day after the election	9 a.m. on the 14th day
Georgia	5 p.m. on the Monday after the election	5 p.m. on the 17th day (non-presidential offices)
Wisconsin	No later than 14 days after	December 1
California	No later than 30 days after (non-presidential offices)	No later than the 38th day
Pennsylvania	Unofficial results by the Tuesday after; final 5 days later if no recount is filed	Not specified in statute

Source: NCSL, Canvass Deadlines, general elections ^[15].

Recounts follow their own rules. In 26 states and Washington, D.C., a recount is automatic when the result falls within a set margin, most often 0.5% ^[16]. Pennsylvania, Arizona and Florida use 0.5%; Ohio uses 0.25% for statewide races; Michigan uses 2,000 votes for statewide races ^[16]. Pennsylvania's 2024 Senate race crossed its threshold, and the state ordered a statewide recount on November 13, 2024 ^[11]. The department halted it after Casey conceded, and counties were to certify by November 25 ^[12]. The AP counts at least 37 statewide recounts since 2000, three of which changed the outcome, all in races decided by hundreds of votes ^[13].

How does DataPorium show election-night results?

DataPorium's election pages at dataporium.tech/elections show certified results for past elections ^[7]. On election night, the pages show the unofficial count as it is reported, label the candidate ahead as "Leading", mark the data as unofficial with the time of the last update, and never show a winner until the race has been called ^[7]. Margins follow the same R+ and D+ convention used for certified results, so a race at R+0.4 with votes still being counted is a lead, not a result.

A margin is the gap between the top two candidates in points, swing is how that gap moved since the last election, and an election-night lead is unofficial until the race is called and certified.

Key takeaways

The margin is the gap between the top two shares in points; Pennsylvania's 2024 Senate race was R+0.2, or 15,115 votes ^[1].
Swing measures movement: the presidential margin moved 5.9 points toward Republicans from 2020 to 2024, while Larimer County, Colorado, moved 2.2 points toward Democrats ^[4]^[6].
Turnout against eligible adults ranged from 77.2% in Minnesota to 49.2% in Hawaii in 2024 ^[7].
Counts shift because states process and accept mail ballots on different schedules: 15 states and Washington, D.C., count some ballots that arrive after Election Day ^[9].
Automatic recounts exist in 26 states and Washington, D.C., most often at a 0.5% margin ^[16].

Frequently asked questions

What does R+5 mean in election results?

It means the Republican candidate's vote share was 5 percentage points higher than the Democratic candidate's. D+5 means the reverse. For example, Arizona voted R+5.5 for president in 2024 ^[4].

Why do election results change after election night?

Mail, early, provisional and late-arriving ballots are counted at different times in different states. Pennsylvania's 2024 Senate lead shrank from 29,338 votes in unofficial returns on November 13 to 15,115 in the certified result ^[1]^[11].

Who calls elections in the United States?

News organizations such as the Associated Press call races when they conclude the trailing candidate cannot catch up. These calls are not official; results become official when states certify them, under deadlines such as the 14th day after the election in Florida ^[13]^[15].

What margin triggers an automatic recount?

It depends on the state. The most common threshold is 0.5%, used in Pennsylvania, Arizona and Florida; Ohio uses 0.25% for statewide races and Michigan 2,000 votes ^[16].