# Days to Years (365 days) (d to yr)

> Convert days to years (365 days): 1 d = 0.00273973 yr. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `days-to-years` · Quantity: Time (`time`, base unit s) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/days-to-years · This document: https://tttkmbb.com/conversion/days-to-years.md · JSON: https://tttkmbb.com/conversion/days-to-years.json (add `?value=` for a result)

## Formula

- `1 d = 0.00273973 yr`
- `years (365 days) = days × 0.002739726027`
- Reverse: `days = years (365 days) × 365`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 d = 0.0136986 yr
- 12.5 d = 0.0342466 yr
- 100 d = 0.273973 yr

## Conversion table

| Days (d) | Years (365 days) (yr) |
| --- | --- |
| 1 | 0.00273973 |
| 2 | 0.00547945 |
| 3 | 0.00821918 |
| 4 | 0.0109589 |
| 5 | 0.0136986 |
| 6 | 0.0164384 |
| 7 | 0.0191781 |
| 8 | 0.0219178 |
| 9 | 0.0246575 |
| 10 | 0.0273973 |
| 15 | 0.0410959 |
| 20 | 0.0547945 |
| 25 | 0.0684932 |
| 30 | 0.0821918 |
| 40 | 0.109589 |
| 50 | 0.136986 |
| 75 | 0.205479 |
| 100 | 0.273973 |
| 200 | 0.547945 |
| 250 | 0.684932 |
| 500 | 1.36986 |
| 1000 | 2.73973 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=day&to_unit=year_365` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"day","to_unit":"year_365"}`
- All time units: https://tttkmbb.com/api/v1/units?quantity=time · full converter: [Time Converter](https://tttkmbb.com/conversion/time.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many years (365 days) are in one day?**

1 d = 0.00273973 yr. The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.

**What is the formula to convert days to years (365 days)?**

Multiply the value in days by 0.002739726027: years (365 days) = days × 0.002739726027. For example, 5 d = 0.0136986 yr.

**How do I convert years (365 days) back to days?**

Multiply by the inverse factor 365 (days = years (365 days) × 365), or use the years (365 days)-to-days page.

## Related conversions

- [Years (365 days) to days](https://tttkmbb.com/conversion/years-to-days.md) (reverse)
- [Hours to Minutes](https://tttkmbb.com/conversion/hours-to-minutes.md)
- [Minutes to Hours](https://tttkmbb.com/conversion/minutes-to-hours.md)
- [Minutes to Seconds](https://tttkmbb.com/conversion/minutes-to-seconds.md)
- [Seconds to Minutes](https://tttkmbb.com/conversion/seconds-to-minutes.md)
- [Days to Hours](https://tttkmbb.com/conversion/days-to-hours.md)
- [Hours to Days](https://tttkmbb.com/conversion/hours-to-days.md)
- [Weeks to Days](https://tttkmbb.com/conversion/weeks-to-days.md)
- [Days to Weeks](https://tttkmbb.com/conversion/days-to-weeks.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)