A patent term calculator is five additions and one lookup. The additions are easy. The lookup is the one that decides whether the answer means anything.
The arithmetic gives you a ceiling — the latest date the patent could possibly expire.
The lookup tells you whether it is still alive, and 58.6% of US utility patents are not, by the time they reach that ceiling.
Do both. A calculation without a maintenance fee check is a common and expensive mistake in patent diligence.
The six inputs
| Input | Where it is printed | Effect |
|---|---|---|
| Earliest non-provisional filing date | Front page field (22); Related U.S. Application Data if there is a chain | Starts the clock |
| Grant date | Front page field (45) | Starts the maintenance fee clock |
| Patent Term Adjustment | Front page, near filing data, in days | Adds |
| Patent Term Extension | Front page notice, pharma and devices only | Adds |
| Terminal disclaimer | Front page notice or file wrapper | Caps |
| Maintenance fee status | USPTO Patent Center | Can end it early |
Three of the six are on the front page. The terminal disclaimer is sometimes only in the file wrapper, and the fee status is never on the document at all.
The calculation, step by step
Step 1 — Find the earliest non-provisional filing date.
Field (22) gives the filing date of the application that issued. If the patent is a continuation, divisional or continuation-in-part, look at Related U.S. Application Data and take the earliest non-provisional date in that chain.
Ignore any provisional. Provisional filing dates appear in the priority data and are never used for the 20-year calculation.
Step 2 — Add twenty years.
That is the base expiry date.
Step 3 — Add the Patent Term Adjustment.
PTA is printed in days. Add them to the base date. Zero is a valid figure and means no adjustment was awarded.
Step 4 — Add any Patent Term Extension.
Only for pharmaceuticals, medical devices, and food and colour additives. Up to five years, capped at 14 years from FDA approval. Most patents have none.
Step 5 — Apply any terminal disclaimer.
If one exists, the patent expires when the referenced earlier patent expires. Calculate that patent's term too, and take the earlier of the two dates.
Step 6 — Check maintenance fee status.
Look the patent up in USPTO Patent Center. If a fee was missed and the grace period has closed, the patent expired then, and every step above is moot.
Worked example 1: a straightforward utility patent
| Step | Value |
|---|---|
| Field (22) filing date | 14 March 2013 |
| Provisional claimed | Yes, March 2012 — ignored |
| Base expiry (+20 years) | 14 March 2033 |
| Patent Term Adjustment | 312 days |
| Adjusted expiry | 20 January 2034 |
| Terminal disclaimer | None |
| PTE | None |
| Grant date | 9 June 2015 |
| Fee 1 due (3.5 yrs) | December 2018 — paid |
| Fee 2 due (7.5 yrs) | December 2022 — paid |
| Fee 3 due (11.5 yrs) | December 2026 — outstanding, $8,280 |
| Answer | Expires 20 Jan 2034 if the third fee is paid |
Two answers, not one. Pay the fee and the patent runs to January 2034. Miss it and the patent ends in mid-2027 at the close of the grace period — nearly seven years earlier.
The provisional cost nothing in term. Filing in March 2012 and converting in March 2013 gave 21 years of protection from first filing rather than 20.
Worked example 2: a continuation with a terminal disclaimer
| Step | Value |
|---|---|
| This patent's own filing date | 2 August 2018 |
| Earliest non-provisional in family | 11 January 2015 (parent) |
| Base expiry (+20 years from parent) | 11 January 2035 |
| Patent Term Adjustment on this patent | 145 days |
| Adjusted expiry | 5 June 2035 |
| Terminal disclaimer | Yes — referencing the parent |
| Parent's expiry | 11 January 2035 (parent had 0 days PTA) |
| Answer | 11 January 2035 — the disclaimer caps it |
The 145 days of PTA were surrendered. The terminal disclaimer cuts the continuation back to the parent's date, so its own adjustment is worthless.
Using this patent's own filing date would have produced August 2038 — three and a half years wrong, in the direction that overvalues the asset.
The common ownership condition also applies. These two patents must stay in the same hands to remain enforceable, so they cannot be sold separately.
Worked example 3: a pharmaceutical patent with PTE
| Step | Value |
|---|---|
| Non-provisional filed | 20 May 2009 |
| Base expiry | 20 May 2029 |
| Patent Term Adjustment | 588 days |
| Adjusted expiry | 28 December 2030 |
| FDA approval | 14 September 2021 |
| PTE granted | 4 years, 2 months |
| Extended expiry | 28 February 2035 |
| 14-year cap from approval | 14 September 2035 |
| Cap binding? | No — extended date is earlier |
| Answer | 28 February 2035 |
Nearly 26 years from filing. PTA and PTE both applied, and the 14-year cap did not bite because the base date was already late enough.
Only one patent per approved product gets PTE. If this drug is also covered by a formulation patent and a method-of-treatment patent, neither of those receives an extension.
Errors that produce wrong answers
| Error | Effect | Fix |
|---|---|---|
| Counting the provisional year | Answer one year too short | Use the non-provisional date |
| Using a continuation's own filing date | Answer years too long | Use the earliest in the family |
| Ignoring Patent Term Adjustment | Answer months to years too short | Read the front page |
| Missing a terminal disclaimer | Answer too long | Check the front page and file wrapper |
| Calculating from the grant date | Wrong for utility patents | Grant date is for design patents and fee timing |
| Skipping the fee check | Answer may describe a dead patent | Patent Center |
| Assuming family members share a date | Wrong per jurisdiction | Calculate each country separately |
Two of these move the answer in opposite directions, which is why errors do not cancel out. Counting a provisional understates term; using a continuation's own filing date overstates it.
The maintenance fee lookup
Fees fall due at 3.5, 7.5 and 11.5 years after the grant date — not the filing date.
| Fee | Due after grant | Large | Small (40%) | Micro (20%) |
|---|---|---|---|---|
| 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 | $14,470 | $5,788 | $2,894 |
Each has a six-month grace period with a surcharge. After that the patent expires permanently and without notice.
Design and plant patents have no fees at all, which is why they almost always run their full term while utility patents mostly do not. See patent maintenance fees for the windows and what happens when one is missed.
What the calculation is for
Three situations, three different uses.
| Situation | What the number tells you |
|---|---|
| You own it | Whether the next fee buys enough remaining window to be worth $8,280 |
| You want to buy it | What you are paying for — remaining life is the multiplier on every other value factor |
| It blocks you | Whether designing around is cheaper than waiting it out |
For a blocking patent, the fee schedule is as informative as the expiry date. A patent approaching its third fee has a real chance of simply being abandoned — 23.2 points of each cohort drops out at that stage.
For a patent you own, the calculation is a decision prompt, not a fact to file away. Remaining life falls every year while the next fee rises, so the answer that was right at 3.5 years is frequently wrong at 11.5. See how long can a patent last for the maximum-term rules and patent expiration date for the edge cases.
Design patents: the one-line calculation
| Filed | Term |
|---|---|
| On or after 13 May 2015 | 15 years from grant |
| Before 13 May 2015 | 14 years from grant |
No PTA, no PTE, no maintenance fees, no terminal disclaimer complications. Grant date plus fifteen years, and it will still be in force on that date.
Prosecution time does not reduce it, because the clock starts at grant. A design patent that took two years to issue still gets its full fifteen years.
Calculating across a portfolio
Doing this once is arithmetic. Doing it for two hundred patents is a process, and it is the process that produces the annual renewal decision.
| Field to capture | Source | Why |
|---|---|---|
| Patent number | — | Key |
| Earliest non-provisional filing | Front page / family data | Term start |
| Grant date | Front page | Fee timing |
| PTA days | Front page | Term addition |
| Terminal disclaimer reference | Front page | Cap, and ownership constraint |
| Calculated expiry | Derived | The ceiling |
| Next fee date and amount | Derived from grant date | The decision trigger |
| Entity status | Filing record | Determines fee amount |
| Practised by anyone? | Your own knowledge | The actual decision input |
Entity status is the field most often stale. Small and micro entity discounts are 60% and 80% respectively, but status has to be true at the time of payment. A company that has grown past the small entity thresholds and keeps paying reduced fees has a problem, not a saving.
Sort by next fee date, not by expiry date. The fee window is the moment a decision is forced; the expiry date is just context for it.
The three-fee structure gives you three review points across a patent's life. Treating each as a genuine decision — keep, sell, or lapse — rather than a default renewal is the whole of portfolio management.
Verifying an expired patent
For freedom-to-operate work, the question is inverted. You are not asking how long a patent lasts; you are asking whether it is safely dead.
| Check | What it rules out |
|---|---|
| Calculated expiry date passed | The obvious case |
| Maintenance fee lapse confirmed in Patent Center | Early death |
| No petition to revive filed | A lapsed patent can be revived under 37 CFR 1.378 |
| No PTE on the record | Pharma patents can run far past the expected date |
| Continuations in the family still pending or granted | The parent expiring does not clear the family |
| Foreign equivalents | Expiry is per jurisdiction |
The revival risk is the one most often missed. A patent that lapsed for unintentional non-payment can be revived by petition with a surcharge. Anyone who started practising the invention during the lapse may hold intervening rights, but relying on that is a worse position than knowing the status.
Family members matter more than the individual patent. A parent expiring tells you nothing about a continuation with different claims that is still in force. Always check the whole family. See freedom to operate for how in-force status drives clearance.
And check the date you did the search. Fee status changes; a clearance opinion is accurate as of the day it was run and no later.
Reading the front page
Every input except fee status is printed on the granted patent, in numbered INID fields that are consistent across jurisdictions.
| Field | Contains | Use in the calculation |
|---|---|---|
| (21) | Application number | Look-up key for Patent Center |
| (22) | Filing date | Start of the 20-year term |
| (45) | Date of patent | Grant date — starts the fee clock |
| (60) | Related US application data | Earlier filings; find the earliest non-provisional here |
| (63) | Continuation data | Confirms the parent to calculate from |
| (30) | Foreign priority | Does not affect US term |
| (73) | Assignee | Ownership at grant only |
| PTA notice | "Subject to a terminal disclaimer" or a day count | Adds or caps |
Field (30) foreign priority is a common false trigger. A foreign priority claim establishes an earlier effective filing date for prior art purposes, but it does not start the 20-year term. The term still runs from the US non-provisional filing.
The terminal disclaimer notice is easy to miss. It appears as a short line of text near the patent data rather than as a numbered field, and it overrides every other calculation.
Field (60) is where continuation chains hide. A patent that looks like a 2019 filing may be a continuation of a 2011 application, making it eight years shorter than it appears.
Patent term calculator: the checklist
- Locate the earliest non-provisional filing date — field (22), or the earliest date in Related U.S. Application Data for a continuation chain.
- Discard the provisional date. It never enters the 20-year calculation.
- Add 20 years for a utility patent. For a design patent, take the grant date and add 15 and stop.
- Add the Patent Term Adjustment in days, from the front page.
- Add Patent Term Extension only for pharmaceuticals, medical devices and food or colour additives — then check the 14-years-from-approval cap.
- Look for a terminal disclaimer. If present, calculate the referenced patent's expiry and take the earlier date.
- Look up maintenance fee status in Patent Center. This is the step that distinguishes a live patent from an expired one.
- Identify the next fee, its amount and its window, and diarise three months before the grace period closes.
- Repeat per jurisdiction for a patent family. Foreign members run on annual renewal fees and expire independently.
- Re-run the whole calculation at every fee deadline, because the decision it supports changes as the remaining window shrinks.