There is no year zero, neither AD (CE) nor BC (BCE). Read bellow about these acronyms.
Below there is a set of steps to follow in order to convert number years to words...
1. For years of four digits (ie: 1000, 1435, 2000, 2018, ...9999)
2. For years of three digits (ie: 100, 137, 209, 357, ...999)
3. For years of one or two digits (ie: 1, 5, 10, 45, 137, 209, 357, ...999)
4. AD, BC, CE, BCE acronyms
1. For years of four digits (ie: 1000, 1435, 2000, 2018, ...9999)
1.1. For years ending with three zeros there is only one way of writing them out:
1000 = the year one thousand, in both American and British English words;
2000 = the year two thousand, in both American and British English words;
3000 = the year three thousand, in both American and British English words;
1.2. For years ending with two zeros there is only one way of writing them out:
1700 = the year seventeen hundred, in both American and British English words;
1900 = the year nineteen hundred, in both American and British English words;
2100 = the year twenty-one hundred, in both American and British English words;
1.3. If only the second and the third digit (hundreds and tens digits) are zeros, there are three ways of writing out the year:
1005 = the year ten oh five, in both American and British English words;
1005 = the year one thousand five, in American English;
1005 = the year one thousand and five, in British English;
2009 = the year twenty oh nine, in both American and British English words;
2009 = the year two thousand nine, in American English;
2009 = the year two thousand and nine, in British English;
1.4. If the second digit (hundreds digit) is zero, there are three ways of writing out the year:
1059 = the year ten fifty-nine, in both American and British English words;
1059 = the year one thousand fifty-nine, in American English;
1059 = the year one thousand and fifty-nine, in British English;
2010 = the year twenty ten, in both American and British English words;
2010 = the year two thousand ten, in American English;
2010 = the year two thousand and ten, in British English;
2018 = the year twenty eighteen, in both American and British English words;
2018 = the year two thousand eighteen, in American English;
2018 = the year two thousand and eighteen, in British English;
1.5. If the third digit (tens digit) is zero, then there are two ways of writing out the year:
1509 = the year fifteen oh nine, in American English;
1509 = the year fifteen hundred and nine, in British English;
1908 = the year nineteen oh eight, in American English;
1908 = the year nineteen hundred and eight, in British English;
1.6. In general, when the second and the third digits of the year are different of zero, write the first two and the second two digits as if they were single numbers. There is only one ways of writing them out:
1870 = the year eighteen seventy, in both American and British English words;
1878 = the year eighteen seventy-eight, in both American and British English words;
1970 = the year nineteen seventy, in both American and British English words;
1973 = the year nineteen seventy-three, in both American and British English words;
2110 = the year twenty-one ten, in both American and British English words;
2115 = the year twenty-one fifteen, in both American and British English words;
2. For years of three digits (ie: 100, 137, 209, 357, ...999)
2.1. For years ending with two zeros, there is only one ways of writing them out:
400 = the year four hundred, in both American and British English words;
600 = the year six hundred, in both American and British English words;
900 = the year nine hundred, in both American and British English words;
2.2. If only the second digit (tens digit) is zero, there are two ways of writing out the year:
105 = the year one oh five, in American English;
105 = the year one hundred and five, in British English;
702 = the year seven oh two, in American English;
702 = the year seven hundred and two, in British English;
2.3. In general, when the second digit of the year is different of zero, write the first digit separately, then the last two as a single number. There are two ways of writing them out:
497 = the year four ninety-seven, in both American and British English words;
497 = the year four hundred and ninety-seven, in British English words;
620 = the year six twenty, in both American and British English words;
620 = the year six hundred and twenty, in British English;