A patent family is every application and patent that grew from one original filing.
They share a specification and a priority date, and they claim different things from it.
Which means the family, not the individual patent, is the meaningful unit. Eight patents in one family protect one invention thoroughly. Eight unrelated patents protect eight things thinly.
And reading the family is the only way to find the real expiry date.
The member types
| Member | Adds new matter? | Priority |
|---|---|---|
| Parent | — | The original |
| Continuation | No | Parent's |
| Divisional | No | Parent's |
| Continuation-in-part | Yes | Split — see below |
| Foreign counterpart | No | Parent's |
| Reissue | No | Original patent's |
| Provisional | — | Starts the priority year, not the term |
Continuations and divisionals share the parent's disclosure entirely. Nothing new can be added, which is why the original specification sets the ceiling for the whole family.
Term runs from the earliest parent
| Filing | Own filing date | Actual expiry |
|---|---|---|
| Parent | 2016 | 2036 |
| Continuation | 2020 | 2036 |
| Continuation | 2023 | 2036 |
| Divisional | 2021 | 2036 |
This is the most misread fact in patent work. A patent filed in 2023 as a continuation of a 2016 application has thirteen years left, not twenty.
Check Related U.S. Application Data on the front page before calculating anything.
Buyers, defendants and sellers all get caught by this, in both directions — sellers overstate the term and defendants overestimate their exposure.
Continuations-in-part are the exception
| Matter | Effective date |
|---|---|
| Carried from the parent | Parent's priority date |
| Newly added in the CIP | CIP's filing date |
| Consequence | Different claims, different dates in one patent |
A CIP claim relying on new matter cannot use the earlier date. Prior art published between the two dates can be cited against those claims and not against the others.
Which makes CIPs harder to assess. Each claim has to be traced to whether its support existed in the parent.
Why families exist
| Reason | Detail |
|---|---|
| Pursue further claims | Continuations, from the same disclosure |
| Respond to a restriction requirement | Divisionals |
| Claim what competitors built | Continuations, written with hindsight |
| Add improvements | CIPs |
| Cover other jurisdictions | Foreign counterparts |
| Build depth against design-arounds | Layered claims |
The hindsight point is the valuable one. A continuation lets you write claims aimed at what a competitor actually launched, which you could not have anticipated at original filing.
Restriction requirements are common. An examiner deciding an application claims several distinct inventions requires an election, and the non-elected claims survive only in a divisional. See non-provisional patent application example.
The window that closes silently
| Continuations may be filed | While a parent is pending |
| Window closes | When the parent issues with nothing pending |
| Reminder | None |
| Reopenable afterwards | No |
| Effect of missing it | The family is closed permanently |
Nothing prompts this decision. The parent grants, which feels like success, and the option disappears at the same moment.
Keeping one continuation pending keeps the family open at the cost of that application's fees, which is frequently worth it.
Reading a family view
| Tool | Shows |
|---|---|
| Espacenet | Family across jurisdictions |
| Google Patents | Related applications, worldwide |
| USPTO Patent Center | US file histories, continuity data |
| Front page, Related U.S. Application Data | The US chain directly |
| INPADOC family | Extended family definition |
| Family type | Definition |
|---|---|
| Simple family | Exactly the same priority documents |
| Extended family | At least one shared priority document |
Most database family views show the extended family, which is broader than you may expect and can include members claiming quite different things.
What each member covers
| Member | Typical claims |
|---|---|
| Parent | Whatever was allowable first |
| Continuation 1 | Broader, or aimed differently |
| Continuation 2 | Written toward a competitor's product |
| Divisional | The non-elected invention |
| Foreign counterparts | Whatever that office allowed |
Foreign members frequently have different claims from the US member, because each office examines independently against its own prior art and practice.
Never assume the German counterpart claims what the US patent claims. Read them.
Reissue and reexamination members
| Type | Purpose |
|---|---|
| Reissue | Correct an error in a granted patent |
| Broadening reissue | Within 2 years of grant only |
| Narrowing reissue | Any time |
| Reexamination certificate | Result of a reexamination |
| Effect on term | Original patent's term |
A reissue takes the original patent's term. Correcting an error does not restart anything.
Broadening reissue has a two-year window from grant, which is another deadline with no reminder attached.
Foreign members run on separate clocks
| US members | Foreign members | |
|---|---|---|
| Expiry | Shared, from the earliest parent | Own national term |
| Renewal | Three maintenance fees | Annual annuities |
| Payable while pending | No | Often yes |
| Missing one affects | That patent | That country only |
A family can be alive in three countries and lapsed in four, and nothing in the US record reveals that.
Each jurisdiction needs checking separately. See patent annuity fees by country.
Worked example: reading a family before buying
A patent offered for sale, described as having "15 years remaining".
| Step | Finding |
|---|---|
| 1. Front page filing date | 2021 |
| 2. Related U.S. Application Data | Continuation of a 2014 application |
| 3. Actual expiry | 2034 — 8 years, not 15 |
| 4. Family view in Espacenet | Parent, 2 continuations, EP and JP members |
| 5. Patent Center on each US member | Parent lapsed 2023; one continuation live |
| 6. Anything pending? | One continuation still pending |
| 7. EP status | Validated in 2 states, 1 lapsed |
What changed in the assessment
| Point | Effect |
|---|---|
| Term overstated by 7 years | Price should reflect 8, not 15 |
| Parent already lapsed | Fewer claims in force than presented |
| Pending continuation | Adds real value — family stays open |
| EP fragmented | Two live national rights, not one European patent |
Steps one to three took five minutes and free tools. The seller was probably not being dishonest; continuation chains are miscalculated constantly.
The pending continuation was the genuinely good news and it had not been mentioned. An open family can still pursue claims aimed at current products.
Terminal disclaimers within a family
| Why filed | Overcome obviousness-type double patenting |
| Effect | Caps the later patent's term to the earlier one |
| Also requires | Common ownership |
| Reversible | No |
| Common in | Families with several related patents |
Terminal disclaimers are routine in deep families and they mean the family expires together even where later members were filed years apart.
Check the front page for one before calculating any member's expiry independently.
Family depth is what buyers value
| Shallow | Deep | |
|---|---|---|
| Members | 1 | 4–8 |
| Claim levels | One | Broad, implementation, method |
| Design-around difficulty | Low | High |
| If one claim is invalidated | Nothing left | Others survive |
| Jurisdictions | US only | Market plus manufacturing |
Depth is why buyers pay more for families than for patents. One broad claim can be invalidated or avoided; a family with claims at several levels leaves fewer routes.
Build it through continuations while the window is open. See patent portfolio.
Worked example: building depth
A company files one application and keeps the family open.
| Year | Action | Result |
|---|---|---|
| 2018 | Non-provisional filed | Parent |
| 2020 | Restriction requirement | Divisional filed |
| 2021 | Parent allowed → continuation filed | Family stays open |
| 2022 | Competitor product launches | Now visible |
| 2022 | Continuation claims written toward it | Hindsight advantage |
| 2024 | Second continuation filed | Family still open |
| All members expire | 2038 | From the 2018 parent |
| Members | 5 US patents |
| Coverage | Broad claim, implementation claims, claims aimed at a real product |
| Design-around difficulty | High |
| Cost | 5 sets of maintenance fees |
The 2022 continuation is the valuable one and it only existed because the family was never allowed to close.
Every member expires in 2038 regardless of filing date, which is the constraint that makes depth worth building early.
The whole family faces the same fee schedule
| Fee | Due after grant | Large | Small | Micro |
|---|---|---|---|---|
| First | 3.5 years | $2,150 | $860 | $430 |
| Second | 7.5 years | $4,040 | $1,616 | $808 |
| Third | 11.5 years | $8,280 | $3,312 | $1,656 |
| Total per member | $14,470 | $5,788 | $2,894 |
Each US member carries its own maintenance fees. A family of five large-entity patents carries over $72,000 across their lives.
| Ipiry Patent Survival Curve v1.0 | Rate |
|---|---|
| Survive the 3.5-year fee (2022 cohort) | 85.8% |
| Survive the 7.5-year fee (2018 cohort) | 64.6% |
| Reach full term (2014 cohort) | 41.4% |
Computed from 27,273,654 USPTO maintenance fee records covering 8,262,336 US utility patents — see the patent survival curve.
Families get pruned member by member. Deciding which to keep is a family-level question, not a per-patent one.
Pruning a family
| Member | Keep if |
|---|---|
| Broadest claims | Almost always |
| Implementation claims | They block real design-arounds |
| Claims aimed at a live product | Yes |
| Divisional on an unused invention | Assess |
| Foreign member in a market you exited | Release |
| Anything pending | Keeps the family open |
Prune at family level, not patent by patent. Releasing the member with the broadest claims to save a fee can devalue everything else.
Patent family: the checklist
- Treat the family as the unit, not the individual patent.
- Read Related U.S. Application Data first. It reveals the real expiry.
- Calculate term from the earliest non-provisional filing in the chain.
- Trace CIP claims individually — new matter gets a later date.
- Check whether anything is still pending. An open family is worth more.
- File a continuation before the parent issues. No reminder exists.
- Use Espacenet for the worldwide view, Patent Center for US status.
- Check each foreign member separately. Statuses diverge.
- Read foreign claims. They differ from the US ones.
- Budget maintenance fees per member, and prune at family level.