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Anniversary Calculator

Counts completed years, months and days since a start date (wedding, job, founding), finds the next anniversary date and the days until it, and names the traditional anniversary gift material for that year.

When to use

You want to know which anniversary is coming up, how many days remain until it, or the traditional gift for a given anniversary year.

Do not use when: You need someone's age (use age) or a general date difference with business days (use date-difference).

Formula

years_completed = calendar years from start_date to as_of_date; next_anniversary = first (month, day) of start_date on or after as_of_date; days_until = next_anniversary − as_of_date

Gregorian calendar arithmetic in UTC. Gift materials follow the common US/UK traditional list (paper, cotton, leather … silver at 25, gold at 50, diamond at 60); years without a traditional material return a note instead.

Inputs

Parameter	Type	Unit	Required	Description
`start_date`	date		yes	Date of the original event (YYYY-MM-DD), e.g. the wedding date.
`as_of_date`	date		default today	Reference date; defaults to the current UTC date.

Outputs

Output	Type	Unit	Description
`years_completed`	integer	years	Full years elapsed on as_of_date.
`elapsed_text`	string		Years, months and days since start_date.
`days_since_start`	integer	days	as_of_date − start_date.
`next_anniversary_date`	date		First anniversary date on or after as_of_date (29 February → 1 March in common years).
`next_anniversary_number`	integer		Ordinal of the next anniversary (e.g. 12 for the 12th).
`next_anniversary_weekday`	string		Day of the week of the next anniversary.
`days_until_next_anniversary`	integer	days	0 when as_of_date is the anniversary itself.
`is_anniversary_today`	boolean		true when as_of_date is an anniversary of start_date.
`traditional_gift`	string		Traditional gift material for the next anniversary year (years 1–15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70).

Example

Wedding 2015-06-20, as of 2026-09-23: {"start_date":"2015-06-20","as_of_date":"2026-09-23"} → {"years_completed":11,"elapsed_text":"11 years 3 months 3 days","days_since_start":4113,"next_anniversary_date":"2027-06-20","next_anniversary_number":12,"next_anniversary_weekday":"Sunday","days_until_next_anniversary":270,"is_anniversary_today":false,"traditional_gift":"Silk"}

Silver wedding: 1999-02-14 as of 2024-02-14: {"start_date":"1999-02-14","as_of_date":"2024-02-14"} → {"years_completed":25,"days_since_start":9131,"next_anniversary_date":"2024-02-14","next_anniversary_number":25,"days_until_next_anniversary":0,"is_anniversary_today":true,"traditional_gift":"Silver"}

GET https://tttkmbb.com/api/v1/calculate/anniversary?start_date=2015-06-20&as_of_date=2026-09-23

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/anniversary (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/anniversary · Markdown: https://tttkmbb.com/time/anniversary.md · JSON definition: https://tttkmbb.com/time/anniversary.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="anniversary"
OpenAPI operationId: calculate_anniversary
Freshness: daily. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Wedding anniversary – traditional gift lists (Wikipedia) (reference)
Gregorian calendar – leap-year rule and month lengths (Wikipedia) (reference)

FAQ

Which anniversary does the gift refer to?

The next one: on 2026-09-23 a couple married on 2015-06-20 has completed 11 years, so the upcoming 12th anniversary (silk) is reported. On the anniversary day itself that day's number is used.

Are modern gift lists included?

No; only the traditional materials. Modern lists (clocks, china, crystal, appliances…) vary by country and retailer.

Related calculators

Age Calculator — The same calculation for a person's birthday.
Days Until Calculator — Countdown to any date.
Date Difference Calculator — Exact difference between two dates including business days.