Methodology and sources

1. Download new incidents. Each morning the pipeline asks every portal for incidents newer than the last one it saw, plus the previous month again, so late reports are picked up.
2. Sort each incident into an offense type. Departments use their own category names. We map them to seven types: homicide; assault and battery; robbery; theft, burglary and robbery; burglary; theft from vehicles; theft; vehicle theft; property damage and arson; weapons offenses; drug offenses. An incident that fits none of them is left out rather than guessed.
3. Count by month. Incidents are counted by the month they occurred, per offense type. Individual records are not kept.
4. Turn counts into rates. Rate per 100,000 per year = incidents in the last 12 months ÷ population × 100,000, using the U.S. Census population. Where a city has fewer than 12 months of usable data the rate is annualized and labelled as such. This is what makes a city of 8 million comparable with one of 2 million, and with the FBI’s figures.
5. Neighborhoods. Where the source records the neighborhood of each incident (Chicago’s 77 community areas), the same counts are kept per area and rated against the area’s 2020 Census population.
6. Publish only complete months. A month is shown once the source’s reporting lag has passed and it holds what a full month holds: at least 85% of a typical month’s incidents on a city’s own portal, 70% for what an agency reports to the FBI. Months held back are listed on the data status page. The current month never appears, and a source that stops updating is labelled historical instead of being shown as current.
7. Check that a year can be a full count. Some agencies send the FBI only part of their cases, every month. Their year looks complete but is far too low, so we give it no rate when homicides are more than 10% of violent crime (across the US they are about 1 to 3%), when violent or property crime is below 15% of the state rate, or when either is zero for the whole year. Those places keep a page with what can be trusted, such as the homicide count and the monthly reports as sent, stay out of the rankings and averages, and are listed on the data status page. An agency whose last complete 12 months ended more than a year before the newest on the site gets no figures until it catches up.

Violent crime on this site is homicide plus assault and battery, and robbery. Property crime is burglary and theft (with robbery where it is not separated yet) together with vehicle theft and property damage. Weapons and drug offenses are counted in the totals but in neither family.

Theft is shown in four lines that add up to the old combined figure. In the cities with their own data we classify each incident from the department’s offense codes or descriptions; for the rest, the same four lines come from what the agency reports to the FBI:

• Robbery: taking property from a person by force or threat, carjacking included. Violent crime, as the FBI counts it.
• Burglary: entering a home, business or other building to steal.
• Theft from vehicles: items or parts taken from a vehicle, break-ins included. The FBI’s national standard (NIBRS) counts a car break-in here, not as burglary, and so do we.
• Theft: everything else taken without force or entry, such as shoplifting, pickpocketing and theft from buildings.

Some police departments file other offenses under theft or larceny. Following the FBI’s national standard (NIBRS), we do not count them as theft, and they are not counted elsewhere on the site either: receiving stolen property, fraud and identity theft (including credit card, bank account and false-promise cases), extortion, embezzlement and theft of services.

Three honest caveats. While a city’s history is being reclassified, or where an agency does not report the detail to the FBI, robbery, burglary and theft stay in one line, “Theft, burglary and robbery”, counted with property crime: a city shows either the old line or the four new ones, never a mix. For cities on FBI figures the four lines are a breakdown only, since the FBI already counts robbery as violent crime and the rates do not change. And “assault and battery” includes simple assaults, which the FBI’s violent index excludes, so our violent rates run higher than FBI figures for the same city. Comparisons between cities on this site use the same rules everywhere, so they remain fair.

• Crime that was never reported to police. Surveys consistently find that a large share of incidents, especially thefts and assaults, are not reported.
• Differences in how departments record. Two cities can classify the same event differently, and a department can change its practice from one year to the next.
• Where in the city it happened. Citywide rates average very different neighborhoods together. Neighborhood-level figures are planned where the source data supports them.
• Population change within a year. Rates use the latest Census estimate for the whole period shown.

Because of all this, treat a difference of a few percent, or a single month’s jump, as noise. The comparison against the same month a year earlier is the most reliable signal on the site.

No names, addresses, photos of people, arrest records or individual incidents, and no pages about specific people. Only monthly counts, which anyone can download from the data status page and reuse with attribution.