The future subjunctive (futuro do subjuntivo) is the form most foreign learners have never met before — many widely-taught Romance languages have lost it, so French and Italian speakers, and English speakers above all, arrive completely unprepared. But Portuguese kept it alive and uses it constantly. The good news mirrors the imperfect subjunctive: it is built from the third-person plural preterite, so if you know eles falaram, eles foram, eles fizeram, you already have everything you need.
The one rule
Take the eles form of the preterite, drop the final -am, and add the future subjunctive endings:
-, -es (regional), -, -mos, -em
In other words: the eu and você/ele/ela forms add nothing to the stem; nós adds -mos; vocês/eles/elas add -em.
| Subject | Ending |
|---|---|
| quando eu | — (bare stem) |
| quando você / ele / ela | — (bare stem) |
| quando nós | -mos |
| quando vocês / eles / elas | -em |
Regular verbs
falar → preterite eles falaram → stem falar-
| Subject | Form |
|---|---|
| quando eu | falar |
| quando você / ele / ela | falar |
| quando nós | falarmos |
| quando vocês / eles / elas | falarem |
comer → eles comeram → stem comer-: comer, comer, comermos, comerem.
partir → eles partiram → stem partir-: partir, partir, partirmos, partirem.
Quando eu falar com ela, eu te aviso.
When I talk to her, I'll let you know.
Se vocês comerem tudo, ganham sobremesa.
If you all eat everything, you get dessert.
Assim que partirmos, te mando mensagem.
As soon as we leave, I'll text you.
The infinitive look-alike trap
Here is the detail that confuses everyone. For regular verbs, the eu and você/ele/ela future subjunctive forms — falar, comer, partir — are spelled and pronounced identically to the infinitive. Quando eu falar uses the same word falar you learned on day one as "to speak."
This is not a coincidence; historically the two forms converged for regular verbs. But they are not the same word, and you can prove it by going to the plural: the future subjunctive inflects, while the infinitive does not. Quando nós falarmos ("when we speak") and Quando eles falarem ("when they speak") show the personal endings -mos and -em that a true infinitive would never take.
| Form | falar | Reveals inflection? |
|---|---|---|
| Infinitive | falar (always invariable) | no |
| Future subj. (eu / você) | falar | looks identical |
| Future subj. (nós) | falarmos | yes — endings appear |
| Future subj. (eles) | falarem | yes — endings appear |
Quando vocês chegarem, a comida vai estar pronta.
When you all arrive, the food will be ready.
Logo que nós terminarmos, vamos sair.
As soon as we finish, we'll go out.
Irregular verbs use the preterite stem
Because the future subjunctive draws on the preterite, irregular verbs are no harder — their irregular preterite stem just carries over. This is also where the form stops looking like the infinitive, which makes the irregularity easy to spot.
| Infinitive | eles (preterite) | Stem | Future subjunctive (eu / nós / eles) |
|---|---|---|---|
| ser / ir | foram | for- | for / formos / forem |
| ter | tiveram | tiver- | tiver / tivermos / tiverem |
| estar | estiveram | estiver- | estiver / estivermos / estiverem |
| fazer | fizeram | fizer- | fizer / fizermos / fizerem |
| poder | puderam | puder- | puder / pudermos / puderem |
| dizer | disseram | disser- | disser / dissermos / disserem |
| trazer | trouxeram | trouxer- | trouxer / trouxermos / trouxerem |
| vir | vieram | vier- | vier / viermos / vierem |
| querer | quiseram | quiser- | quiser / quisermos / quiserem |
Notice how ser and ir again share a form (for, from foram), and how the irregular stems (tiver-, fizer-, for-) are obviously not the infinitive — for is nothing like ser or ir, and fizer is nothing like fazer. That visible difference is your cue that you are dealing with the future subjunctive.
Se você puder, me liga mais tarde.
If you can, call me later.
Quando eu tiver tempo, eu leio esse livro.
When I have time, I'll read that book.
Assim que eu souber de algo, eu te conto.
As soon as I know something, I'll tell you. (saber → souberam → souber)
Why the preterite-stem rule is worth its weight
This is the third tense (after the imperfect subjunctive) built straight off the eles preterite. The payoff for memorizing those preterite forms keeps compounding: one set of irregular preterites gives you the preterite itself, the entire imperfect subjunctive, and the entire future subjunctive. English offers no scaffolding here at all — it has no future subjunctive and simply uses the present indicative ("when I arrive"), which is precisely why the next page on usage matters so much.
Common Mistakes
❌ Quando eu falarei com ela...
Incorrect — 'falarei' is future indicative; time conjunctions take the future subjunctive.
✅ Quando eu falar com ela...
When I talk to her...
The future indicative ending -ei feels right to English speakers thinking "I will talk," but quando triggers the future subjunctive falar.
❌ Quando nós chegar lá, ligamos.
Incorrect — the nós form must inflect: chegarmos.
✅ Quando nós chegarmos lá, ligamos.
When we get there, we'll call.
Because the singular looks like the infinitive, learners mistakenly leave it invariable. The plural must take its endings: chegarmos, chegarem.
❌ Se ele tiver razão... usando 'ter' como infinitivo: Se ele ter razão.
Incorrect — 'ter' (infinitive) can't replace the inflected future subjunctive.
✅ Se ele tiver razão, eu peço desculpas.
If he's right, I'll apologize.
❌ Quando eu fazer o jantar...
Incorrect — 'fazer' is irregular; the stem is 'fizer-' from 'fizeram'.
✅ Quando eu fizer o jantar...
When I make dinner...
Regular verbs let you reuse the infinitive form, but irregular verbs do not — fazer becomes fizer, ter becomes tiver, ser/ir become for.
❌ Assim que eles vierem... escrito 'virem' pensando no infinitivo 'vir'.
Watch the spelling — the form is 'vierem', built on the preterite stem 'vier-'.
✅ Assim que eles vierem, a gente começa.
As soon as they come, we'll start.
Key Takeaways
- Build the future subjunctive from the third-person plural preterite: chop -am, add — / -mos / -em.
- For regular verbs the singular looks like the infinitive (falar, comer), but the plural (falarmos, falarem) reveals it is inflected.
- Irregular verbs use the preterite stem: foram → for, tiveram → tiver, fizeram → fizer — these clearly differ from the infinitive.
- Ser and ir share the form for.
Now practice Portuguese
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Start learning Portuguese→Related Topics
- Futuro do Subjuntivo: UsageA2 — When to use the future subjunctive in Brazilian Portuguese — the obligatory form after 'quando', 'se', 'enquanto', 'assim que' and other time conjunctions pointing to the future.
- Imperfeito do Subjuntivo: FormationB1 — How to build the imperfect subjunctive in Brazilian Portuguese — the single most predictable irregular form, derived directly from the third-person plural preterite.
- Personal vs Impersonal InfinitiveB1 — How to decide whether to leave the infinitive bare or inflect it for person — the rule turns on whether the infinitive has its own, distinct subject.
- The Subjunctive in BR Portuguese: OverviewA2 — What the subjunctive is, why Brazilian Portuguese keeps all three of its tenses fully alive, and what triggers it.
- Future Subjunctive vs Future IndicativeB1 — Why 'quando você chegar' (future subjunctive) pairs with a main-clause future like 'eu vou te ligar' — how the two halves of a future sentence each pick their own form.