# Power reserve explained: 40 hours vs 80 hours

Source: https://lumeandbezel.com/blog/automatic-watch-power-reserve-explained
Published: 2026-10-09
Publisher: Lume & Bezel

**Short answer:** Power reserve is how long a fully wound automatic keeps running once you stop wearing it. A 40 hour watch taken off on Friday evening usually stops some time on Sunday. An 80 hour watch, such as one with Tissot's Powermatic 80 or Hamilton's H-10, is still running on Monday morning. Wearing it only partly winds it, so real run time is often shorter than the listed figure.

Power reserve is one of the few numbers on an automatic's spec sheet that changes how the watch fits your routine. This page explains what the figure means, why a watch often stops sooner than its rating, and how 40 hour and 80 hour movements compare for someone who wears a watch on weekdays and swaps on weekends. It uses power reserve figures from current listings and maker specs. If you are still learning how automatics work, start with [what is an automatic watch](https://lumeandbezel.com/blog/what-is-an-automatic-watch).

## What power reserve means

An automatic watch stores energy in its mainspring. Power reserve is the time the watch runs from a fully wound spring with no further winding. When the spring runs down, the balance stops and the hands stop with it. Nothing is damaged; you wind and reset the watch and it carries on.

The figure assumes a full wind. A watch worn for a quiet day at a desk may not get there, which is why many owners find their watch stops earlier than the spec sheet suggests. Giving the crown some turns in the morning, on movements that hand wind, tops it up.

## Power reserve of common movements

The figures below come from current listings or maker spec pages for the named calibers.

| Movement | Found in | Listed power reserve |
| --- | --- | --- |
| Seiko 4R35 / 4R36 | Seiko 5 Sports, Prospex, Presage | about 41 hours |
| Seiko 4R34 GMT | Seiko 5 Sports GMT SSK001 | 41 hours |
| Orient F6922 | Orient Kamasu, Mako | 40 hours |
| Citizen (Tsuyosa NJ0150) | Citizen Tsuyosa | 42 hours |
| Bulova 8N26 / 82S0 | Bulova Sutton | 42 hours |
| Seiko 6R35 | Seiko Prospex SPB121 | 70 hours |
| Tissot Powermatic 80 | Tissot PRX, Seastar, Le Locle | up to 80 hours |
| Hamilton H-10 | Hamilton Khaki Field Automatic | 80 hours |
| Hamilton H-50 (hand wound) | Hamilton Khaki Field Mechanical | 80 hours |

Listed power reserve by movement

## 40 hours vs 80 hours in a real week

The difference shows up when you take the watch off. Say you wear one automatic Monday to Friday and something else at the weekend. You take it off at 7 pm on Friday.

A 40 hour watch fully wound at that point would stop around 11 am on Sunday. On Monday you need to wind it, set the time and, if it has one, fix the date. An 80 hour watch would still be running at 7 am on Monday, so you put it on and go. If you rotate between two or three watches, the longer reserve saves a lot of resetting.

For someone who wears one watch every day, the gap matters much less. Either movement is topped up each time you wear it, and a 40 hour watch survives a night on the nightstand easily.

- **Around 40 hours:** fine for daily wear, stops over a weekend off the wrist.
- **Around 70 to 80 hours:** survives a full weekend, useful if you rotate watches.
- **Any reserve:** a [watch winder](https://lumeandbezel.com/best/best-watch-winders) keeps it running indefinitely if you prefer not to reset.

## Why your watch may stop sooner than its rating

Most complaints about short power reserve come down to a partly wound mainspring. A rotor needs steady arm movement to wind fully. Desk work, driving and wearing the watch for a few hours a day may not keep up with what the watch uses.

Other causes include magnetism, which can make a watch run erratically, and an old movement whose oils have dried, which costs energy. If a watch stops after a full manual wind and a fraction of its rated time, it may need a service. See [automatic watch keeps stopping](https://lumeandbezel.com/blog/automatic-watch-keeps-stopping) for a step by step check.

1. Hand wind the watch fully from stopped, if the movement allows it.
2. Set the time and leave it still, dial up.
3. Note when it stops. If it runs close to the listed reserve, the movement is fine and the issue was partial winding.
4. If it stops far short, have it checked by a watchmaker.

## Does power reserve affect accuracy

Many movements run most evenly in the upper part of their reserve and drift more as the spring runs low. That is one reason a watch worn every day often keeps steadier time than one left to run down. Exact behavior varies by movement and is not something most listings report.

If accuracy matters to you, keep the watch wound. Wearing it daily, giving it a few crown turns in the morning or using a winder all keep the spring in its better range. For general accuracy ranges, read [how accurate should an automatic watch be](https://lumeandbezel.com/blog/how-accurate-should-an-automatic-watch-be).

[Swiss automatics with 80 hour reserves](https://lumeandbezel.com/best/best-swiss-automatic-watches-under-1000)

## Frequently asked questions

**How long does an automatic watch run when not worn?** Until its power reserve runs out, often 40 to 42 hours for affordable Japanese movements and up to 80 hours for movements like Tissot's Powermatic 80. A partly wound watch runs for less.

**Is an 80 hour power reserve worth paying for?** If you rotate watches or take one off for the weekend, yes, it saves resetting. If you wear one watch every day, a 40 hour reserve is usually enough.

**Does a longer power reserve mean a better watch?** Not by itself. It is a convenience feature. Accuracy, build quality and serviceability matter as much.

**How do I know how much power reserve is left?** Some watches have a power reserve indicator, such as the Seiko Presage SSA459 and some Orient Star models. On others, you can only judge by how long it has been off the wrist.

## Gear guides for this topic

- https://lumeandbezel.com/best/best-swiss-automatic-watches-under-1000
- https://lumeandbezel.com/best/best-tissot-automatic-watches
- https://lumeandbezel.com/best/best-watch-winders