There are not very many verbs that are irregular in the future tense. The ones that are irregular will use a different stem, but the endings added on will still be the regular endings for the future tense. (Remember that with regular verbs in the future tense, the ending is added on to the infinitive.)
Notice that in the first grouping, the stem is made by dropping the final vowel of the infinitive and replacing it with a “d”. In the second grouping, the final vowel is simply removed and not replaced with anything.
| VERB poner salir tener valer venir caber poder saber decir hacer querer | NEW STEM pondr- saldr- tendr- valdr- vendr- cabr- podr- sabr- dir- har- querr- | pondré, etc. saldré, etc. tendré, etc. valdré, etc. vendré, etc. cabré, etc. podré, etc. sabré, etc. diré, etc. haré, etc. querré, etc. |