A torsion spring is rated in cycles, not years — one up and one down is a cycle. Count the daily cycles, subtract what a door has already spent, and the spreadsheet tells you how much life is left before the spring lets go.
A 10,000-cycle spring cycled 4 times a day for 5 years has used 7,300 cycles; the remaining 2,700 last about 1.8 more years.
The example
Three doors with different ratings and daily use. Days installed is the age of the current spring.
| A | B | C | D | E | F | |
|---|---|---|---|---|---|---|
| 1 | Door | Rated | Per day | Days in | Used | Years left |
| 2 | Main door | 10000 | 4 | 1825 | 7300 | 1.8 |
| 3 | Side door | 10000 | 6 | 1460 | 8760 | 0.6 |
| 4 | Shop door | 20000 | 8 | 1900 | 15200 | 1.6 |
The formula
Used cycles are the daily rate times the days installed; the leftover divided by yearly cycles gives the years:
How it works
Two multiplications frame one subtraction:
C2*D2is cycles used — 4 a day for 1,825 days is 7,300.B2-...subtracts that from the rating to get the cycles still in the spring.C2*365is a year's worth of cycles at the current pace.- Dividing the two gives the years of life remaining at today's usage.
Usage is the big lever. Doubling the daily cycles roughly halves the years left, which is why a busy shop door on a 10,000-cycle spring is a yearly replacement.
Try it: interactive demo
Enter the spring rating, cycles per day, and how many days it has been installed.
Variations
Flag springs near end of life
Warn when less than a year remains so it gets scheduled, not stranded.
Percent of life used
Show how much of the rating is spent.
Pitfalls & errors
A cycle is a full open-and-close. Do not count each direction separately or you will double the usage and condemn good springs.
High-cycle springs (25,000 and up) cost a little more but pay off on any door that runs more than a few times an hour. Keep the rating in a cell so upgrades are one edit.
Practice workbook
Frequently asked questions
How many cycles is a standard spring?
Should both springs be replaced together?
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