# BC to AD Calculator

URL: https://speedycalculator.com/calculators/everyday-life/bc-to-ad/
Last updated: 2026-10-25

> The BC to AD calculator works out the number of years between a date BC (BCE) and a date AD (CE) – remembering there is no year zero – and how long ago a BC year was.

## Inputs

- First year
- Era
- Second year
- Era

## Results

- First year (astronomical)
- Second year (astronomical)
- Years between
- First year was this many years ago
- Centuries between

## Formula

```
Astronomical year: AD y → y; BC y → 1 − y
Years between = later astronomical year − earlier astronomical year
BC → AD span = BC year + AD year − 1
```

## Explanation

The Anno Domini system jumps straight from 1 BC to AD 1 – there is no year 0. So from 1 BC to AD 1 is one year, and from 500 BC to AD 500 is 999 years, not 1,000. Astronomers use a year 0 (1 BC = 0) to make arithmetic simple.

### How to use the BC to AD Calculator

- **First year**
- **Era**
- **Second year**
- **Era**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the first year and choose BC or AD, then the second year and its era.

### Tips

- Check whether the end date should be included – event durations usually include it, elapsed time does not.
- Months have 28–31 days, so "one month" is counted by calendar date, not as 30 days.
- Use 24-hour time or set AM/PM carefully when entering clock times.
- Time zones and daylight-saving changes are not applied unless the calculator says so.

### Common mistakes to avoid

- Counting a 30-day month when a calendar month is meant (or the reverse).
- Forgetting leap years when counting days across February.
- Mixing decimal hours (7.5 h) with clock time (7:30).

### Inputs explained

FieldWhat to enterFirst yearA numberEraChoose one: BC / BCE, AD / CESecond yearA numberEraChoose one: BC / BCE, AD / CE

### What each result means

- **Years between** = abs([Second year (astronomical)] - [First year (astronomical)])
- **First year was this many years ago** = year(today()) - [First year (astronomical)]
- **Centuries between** = abs([Second year (astronomical)] - [First year (astronomical)])÷100

### Example values

How the main result changes when **First year** changes and everything else stays at the example values above:

First yearYears between376.5852564.751,0407531,228941.251,4161,129.51,6051,5061,981

## Worked example

Inputs — First year: 753; Era: BC / BCE; Second year: 476; Era: AD / CE.

Results — First year (astronomical) = -752; Second year (astronomical) = 476; **Years between = 1,228**; First year was this many years ago = 2,778; Centuries between = 12.28.

## FAQ

**How many years between 753 BC and AD 476?**
1,228 years (753 + 476 − 1).

**Is there a year 0?**
Not in the BC/AD system; astronomers count 1 BC as year 0.

**Are BCE and CE different from BC and AD?**
No – they are the same years with religiously neutral names.

**What formula does the BC to AD Calculator use?**
Astronomical year: AD y → y; BC y → 1 − y.